What do the Grade 11 Physics cards cover?

36 cards across 7 chapters of the national textbook: Physics and Human Society, Vectors, motion in one and two dimensions, Dynamics, Heat Conduction and Calorimetry, Electrostatics and Electric Circuit and Nuclear Physics. You can take any chapter one card at a time on the page itself.

Is there a national exam in Grade 11?

No. Ethiopia sets national exams in Grade 6, Grade 8 and Grade 12 only. These cards are for your school's own exams, and for the national exam that comes a few years later.

Where do these cards come from?

They are drafted from Grade 11 Physics, the Ministry of Education textbook for this grade. A second pass that cannot see the chapter then re-derives every formula, constant and table row, and anything it cannot confirm is held back instead of published.

Yes. Every card here is free to read and the printable sheet is free to download. Neither needs an account.

When was this last checked?

12 October 2026. Cards arrive chapter by chapter, and the line under each one says when that card was last read through.

Free short notes and revision cards

Grade 11 Physics

Grade 11 Physics on Temari has 36 revision cards, arranged by the chapters of the Ethiopian national curriculum. Every card says when the rule applies, what each symbol in it stands for, and the mistake students most often make with it. They are free to read and need no account.

36
Cards: 7
Chapters: 17
Formulas: 13
Reference tables: Grade 11 Physics
Textbook: Free
Price: 12 October 2026
Last checked

Everything36Formula16Reference table13Common mistake6Rule1

Across the whole subject

Telling heat and temperature apartReference tableWhat it is · Where it lives · SI unit · +5

What is compared	Heat	Temperature
What it is	Energy that moves from a hotter body to a colder one.	The degree of hotness or coldness of a body.
Where it lives	Nowhere. A body stores internal energy, and heat is the name for that energy only while it crosses a boundary.	In the body itself, as a property you can read at any moment.
SI unit	Joule (J). Also the calorie, where 1 cal is about 4.186 J.	Kelvin (K). Also degrees Celsius and degrees Fahrenheit.
Does the amount matter	Yes. Heating more mass takes more heat, so a pot of boiling water needed far more than a cup.	No. The cup and the pot both sit at 100 °C.
What it depends on	The mass, the specific heat capacity of the substance, and the temperature change.	The average translational kinetic energy of one particle, not the total for the whole sample.
How you measure it	Indirectly, with a calorimeter, from measured temperature changes and known specific heat capacities.	Directly, with a thermometer.
What zero means	No net heat crosses between two bodies that are already at the same temperature.	0 K is absolute zero and has never been reached, and kelvin values are never negative. 0 °C is an ordinary temperature, the freezing point of water.
The formula	$Q = mc\,\Delta T$ while the temperature changes, $Q = mL$ while the substance changes state.	Read off the scale. A change of 1 °C is the same size as a change of 1 K.

When you use it

Reach for this when a question treats heat and temperature as one word: how much energy warms a mass of water, why the reading stops climbing while ice melts, or why two bodies stop exchanging energy once they are equally hot.

Watch out

Two mistakes cost marks here. The first is using $Q = mc\,\Delta T$ while ice is melting or water is boiling. The temperature stays put during a change of state, so $\Delta T$ is zero and the formula returns zero heat. The right one is $Q = mL$ , and warming ice at -10 °C into steam is several separate steps rather than one. The second is turning a temperature CHANGE into kelvin by adding 273. Water warmed from 20 °C to 70 °C has changed by 50, in °C and in K alike. Add 273 to a temperature, never to a difference.

Conduction and convection comparedReference tableWhat it is · Where it works · How the energy travels · +5

What is compared	Conduction	Convection
What it is	Heat moving through a material while the material itself stays where it is.	Heat carried by the bulk movement of a fluid.
Where it works	In solids, liquids and gases.	In liquids and gases only, because only a fluid can flow.
How the energy travels	From particle to particle by vibration and collision. In a metal, free electrons carry most of it, which is why metals beat wood and water.	The hot fluid itself moves and takes the energy with it, so warm fluid rises and cool fluid sinks. Natural convection is driven by the density difference heating creates, forced convection by a fan or a pump.
Rate law	Fourier's law: $\dfrac{Q}{t} = kA\dfrac{\Delta T}{L}$ , where L is the thickness measured along the direction of flow.	Newton's law of cooling: $\dfrac{Q}{t} = hA(T_s - T_f)$ , where $T_s$ is the surface temperature and $T_f$ that of the bulk fluid.
Unit of the coefficient	k is in $\text{W m}^{-1}\text{K}^{-1}$ , because the conduction law divides by the thickness L.	h is in $\text{W m}^{-2}\text{K}^{-1}$ . There is no L anywhere in the convection law.
Which is faster	Inside one fluid it is the slower of the two. Along a copper bar it beats convection in still air easily, so this is not a universal rule.	Inside one liquid or gas it normally moves heat faster, because the material carries the energy with it.
Across a vacuum	It cannot cross one. Conduction needs matter.	It cannot cross one either. Only radiation crosses empty space.
Everyday examples	A metal spoon warming in hot tea, the base of a cooking pan, the fins of a heat sink.	Water circulating in a boiling pot, land and sea breezes, warm air rising in a room.

When you use it

Use when a question asks how heat gets from one place to another and you have to name the mode, or when you have to put a number on it with Fourier's law or Newton's law of cooling. The medium decides: a solid can only conduct, while a liquid or a gas does both.

Watch out

Two mistakes cost a mark. The first is copying k's unit onto h and writing the convective coefficient as $\text{W m}^{-1}\text{K}^{-1}$ . Divide the law out instead of memorising it: $h = \dfrac{Q/t}{A\,\Delta T}$ , which is $\text{W m}^{-2}\text{K}^{-1}$ . k keeps the extra metre only because the conduction law divides by the thickness L, and there is no L in the convection law at all. The second is answering that conduction works in a vacuum because two solids can touch. It does not. Both modes need matter, and radiation is the only one that crosses empty space, which is why a vacuum flask still loses heat and why the Sun reaches us at all.

Inertia and momentum comparedReference tableWhat it is · Whose it is · When it is there · +6

What is compared	Inertia	Momentum
What it is	The property by which a body resists any change in its state of rest, or of uniform motion in a straight line.	The quantity of motion a body has because of its mass and its velocity.
Whose it is	A property of the body itself, and mass is the measure of it.	A quantity the body has only while it is moving.
When it is there	Always, at rest and in motion alike.	Zero for a body at rest in the frame you are working in, and there as soon as the body moves in that frame.
How it is measured	By mass, so inertia is proportional to m. Mass is a scalar, in kilograms.	$p = mv$ , in $\text{kg m s}^{-1}$ . That is the same unit as the newton second, since $1\,\text{N} = 1\,\text{kg m s}^{-2}$ .
Dimension	Mass, the measure of inertia, carries $[M]$ .	$[M L T^{-1}]$ , mass times velocity.
Direction	It has none. Mass is a scalar.	It is a vector, pointing along the velocity.
What it depends on	In straight line motion, on the mass alone.	On the mass and the velocity together, so a light bullet can carry as much as a heavy body moving slowly.
How it changes	Only if the mass changes, as it does for a rocket burning fuel.	Whenever a net external force acts, and the change equals the impulse of that force.
Everyday examples	A standing passenger falls backwards when the bus starts and forwards when it brakes. Dust leaves a beaten carpet because the dust stays behind.	A moving car, a kicked football and a fired bullet all carry it.

When you use it

Use when a question puts the two words in one sentence: why a parked lorry is hard to push, why a passenger lurches when a bus starts, or what a moving body hands over in a collision. The inertia compared here is the straight line kind, measured by mass, which is a different quantity from the moment of inertia a turning body has.

Watch out

Students hear that a heavy lorry has huge inertia and write that a parked lorry has huge momentum. A body sitting still has all of its inertia and exactly zero momentum, because $p = mv$ and v is zero. The same confusion turns the bus the wrong way round: when the bus starts your body stays at rest and you fall backwards, and you are thrown forwards only when it brakes. Check the velocity before you claim momentum, and ask which way the vehicle is changing speed before you say which way the passenger falls.

Choosing the right equation of motionReference tablev = u + at · s = ut + 1/2at^2 · v^2 = u^2 + 2as · +1

Equation	The quantity it leaves out	Reach for it when
$v = u + at$	$s$	no distance is given or wanted
$s = ut + \tfrac{1}{2}at^{2}$	$v$	the final velocity is unknown
$v^{2} = u^{2} + 2as$	$t$	no time is given or wanted
$s = \left(\dfrac{u+v}{2}\right)t$	$a$	the acceleration is unknown

When you use it

Use for any body moving in a straight line with constant acceleration. List what the question gives you, spot the quantity it never mentions, and take the equation that leaves that quantity out.

Watch out

All four hold only while the acceleration stays constant. A body on a curve, or one whose acceleration changes, needs calculus instead. Take displacement, velocity and acceleration as positive in one direction and negative in the other, or a body thrown upwards gives an answer with the wrong sign.

Newton's laws and momentumReference tableNet force on a mass · Force from momentum · Action and reaction · +3

What you are finding	Formula	Conditions it holds under
Net force on a mass	$F_{net} = ma$	mass constant, $F$ the resultant
Force from momentum	$F_{net} = \dfrac{\Delta p}{\Delta t}$	holds even when mass changes
Action and reaction	$F_{12} = -F_{21}$	always, on two different bodies
Linear momentum	$p = mv$	a vector, along the velocity
Impulse	$J = F\,\Delta t = \Delta p$	constant force over $\Delta t$
Weight	$W = mg$	$g$ is local, not a constant of nature

When you use it

Use when a question asks what a force does to a body: how fast it speeds up, how hard two bodies push on each other, or what a collision leaves behind. Momentum is conserved in every collision; kinetic energy is conserved only in an elastic one.

Watch out

The two forces of the third law act on two different bodies, so they never cancel each other out. Students subtract them from one another and get zero acceleration for a book resting on a table, when the pair that actually balances is the table's push and the Earth's pull, both acting on the book.

Work, energy and powerReference tableWork by a constant force · Kinetic energy · Gravitational potential energy · +4

What you are finding	Formula	Conditions it holds under
Work by a constant force	$W = Fs\cos\theta$	$\theta$ between force and displacement
Kinetic energy	$KE = \tfrac{1}{2}mv^{2}$	speeds well below light speed
Gravitational potential energy	$PE = mgh$	near the ground, $g$ uniform
Work and energy theorem	$W_{net} = \Delta KE$	always, for any net force
Average power	$P = \dfrac{W}{t}$	work done over a whole interval
Instantaneous power	$P = Fv\cos\theta$	at one moment
Efficiency	$\eta = \dfrac{\text{useful output}}{\text{total input}}$	never greater than 1

When you use it

Use when a question gives you distances and speeds but no time, or asks how much fuel, food or electricity a job costs. The work and energy theorem is often a shortcut past the equations of motion, because it never asks how long anything took.

Watch out

A force at right angles to the motion does no work at all, so the tension in a string swinging a stone in a circle adds no energy however fast it goes. The cosine is what carries this, and dropping it is the commonest lost mark in the topic.

Turning motion read off straight line motionReference tables · v = s/t · a · +4

Straight line	Turning	What changes
$s$	$\theta$	metres become radians
$v = \dfrac{s}{t}$	$\omega = \dfrac{\theta}{t}$	$v = r\omega$
$a$	$\alpha$	$a = r\alpha$
$m$	$I = \sum mr^{2}$	mass becomes moment of inertia
$F = ma$	$\tau = I\alpha$	force becomes torque
$p = mv$	$L = I\omega$	momentum becomes angular momentum
$KE = \tfrac{1}{2}mv^{2}$	$KE = \tfrac{1}{2}I\omega^{2}$	the same energy, counted round an axis

When you use it

Use when a wheel, a disc or a rod turns about a fixed axis. Every equation you already know for straight line motion has a turning twin, so solve the rotating problem by writing the straight line one and swapping each quantity for its partner in this table.

Watch out

The angle must be in radians before any of the links between the two columns holds. A question given in degrees or in revolutions per minute has to be converted first, and forgetting that is what makes an answer come out a factor of 57 too large.

Moment of inertia of common bodiesReference tableThin rod, length L · Hoop or thin ring, radius r · Solid disc or cylinder, radius r · +2

Body	Axis	Moment of inertia
Thin rod, length $L$	through the centre, across the rod	$\tfrac{1}{12}mL^{2}$
Thin rod, length $L$	through one end, across the rod	$\tfrac{1}{3}mL^{2}$
Hoop or thin ring, radius $r$	through the centre, along the axis	$mr^{2}$
Solid disc or cylinder, radius $r$	through the centre, along the axis	$\tfrac{1}{2}mr^{2}$
Solid sphere, radius $r$	through a diameter	$\tfrac{2}{5}mr^{2}$
Hollow sphere, radius $r$	through a diameter	$\tfrac{2}{3}mr^{2}$

When you use it

Use whenever a torque question needs a number for I, or when two bodies race down a slope and you have to say which reaches the bottom first. The smaller the fraction, the closer the mass sits to the axis and the easier the body is to spin.

Watch out

Each of these belongs to one axis only. The same rod is three times harder to swing about its end than about its middle, and reading the wrong row is the usual error. For any other axis parallel to one of these, add $md^{2}$ , where d is the distance between the two axes.

The two conditions for equilibriumRule

\sum F = 0 \quad \text{and} \quad \sum \tau = 0

\sum F = 0 \quad \text{and} \quad \sum \tau = 0

$\sum F$: the sum of every force on the body, taken direction by direction $\mathrm{N}$
$\sum \tau$: the sum of every turning effect about any one chosen point $\mathrm{N\,m}$

When you use it

Use for a ladder against a wall, a beam on two supports, a signboard on a bracket: anything at rest or moving steadily. Both conditions must hold at once, which is what lets you find two unknown forces from one diagram.

Watch out

The first condition alone is not enough. Two equal and opposite forces applied at different points sum to zero and still spin the body, which is why a steering wheel turns. Take moments about the point where an unknown force acts and that force drops out of the equation, leaving one unknown to solve for.

Fluids at rest and in motionReference tablePressure · Pressure at a depth · Upthrust · +2

What you are finding	Formula	Conditions it holds under
Pressure	$P = \dfrac{F}{A}$	force at right angles to the area
Pressure at a depth	$P = \rho g h$	gauge pressure, fluid at rest
Upthrust	$F_{b} = \rho_{f}\,g\,V_{disp}$	$\rho_{f}$ is the FLUID's density
Flow rate stays equal	$A_{1}v_{1} = A_{2}v_{2}$	one pipe, nothing leaking out
Bernoulli	$P + \tfrac{1}{2}\rho v^{2} + \rho g h = \text{constant}$	steady flow, no viscosity

When you use it

Use for anything floating, sinking, or flowing through a pipe: a dam wall, a hydraulic jack, a boat, water speeding up through a narrow section.

Watch out

The density in the upthrust equation is the fluid's, not the object's, and the volume is the volume pushed aside rather than the whole object. A block half under water displaces half its own volume. Depth pressure also depends on depth alone, so a narrow tube and a wide lake at the same depth read the same.

Stress, strain and Young's modulusReference tableStress · Strain · Young's modulus · +2

What you are finding	Formula	Conditions it holds under
Stress	$\sigma = \dfrac{F}{A}$	force spread over the cross section
Strain	$\epsilon = \dfrac{\Delta L}{L_{0}}$	a ratio, so it has no unit
Young's modulus	$E = \dfrac{\sigma}{\epsilon}$	below the elastic limit only
Extension of a wire	$\Delta L = \dfrac{FL_{0}}{AE}$	same conditions as above
Energy stored	$U = \tfrac{1}{2}F\,\Delta L$	the work the stretch cost

When you use it

Use when a wire, cable or beam is stretched and the question asks how far it gives, how much load it will take, or which of two materials is stiffer.

Watch out

Young's modulus belongs to the material and not to the piece: a thick steel cable and a thin steel wire share one value of E, and it is the area in the equation that makes the thick one stretch less. Past the elastic limit the ratio stops being constant and none of these rows holds any more.

Physics and Human Society

A priori and a posteriori knowledgeCommon mistake

When you use it

When asked to classify a statement as knowledge that comes from experience or knowledge that comes from reason, such as mathematics and logic.

Watch out

Mathematical truths such as 2+2=4 are a priori knowledge supplied by reason, even when an example with apples is used to illustrate them. Do not label them a posteriori just because the example uses real objects.

Drafted from Grade 11 Physics, pages 1-16, then checked twice before it went up

Boiling point of water at altitudeReference table150 · 305 · 610 · +1

Altitude (m)	Boiling point of water (°C)
150	99.5
305	99
610	98
1524	95

When you use it

When a question gives or asks for the boiling point of water at a given height, or asks how altitude changes the boiling point.

Drafted from Grade 11 Physics, pages 1-16, then checked twice before it went up

Vectors

Angle from tan inverse needs the correct quadrantCommon mistake

When you use it

Use this when you find the direction of a resultant from tan inverse of R_y over R_x and report it as an angle from the x axis.

Watch out

A calculator tan^-1 gives an angle only between -90 and 90 degrees. Check the signs of R_x and R_y on the xy plane and place the angle in the correct quadrant. For example, a negative R_x with a positive R_y lies above the negative x axis, not the positive x axis.

Drafted from Grade 11 Physics, pages 17-46, then checked twice before it went up

Components of a vectorFormula

A_x=A\cos\theta \qquad A_y=A\sin\theta

A_x=A\cos\theta \qquad A_y=A\sin\theta

$A$: magnitude of the vector $same as the vector, e.g. m or N$
$\theta$: angle measured from the positive x axis $\degree$
$A_x$: x component of A $same as the vector, e.g. m or N$
$A_y$: y component of A $same as the vector, e.g. m or N$

When you use it

Use this to resolve a vector into its x and y components when the angle is measured from the positive x axis.

Watch out

If the angle is measured from the y axis instead, the cosine goes with the y component and the sine with the x component.

Drafted from Grade 11 Physics, pages 17-46, then checked twice before it went up

Magnitude of a resultant from its componentsFormula

R=\sqrt{R_x^{2}+R_y^{2}}

R=\sqrt{R_x^{2}+R_y^{2}}

$R$: magnitude of the resultant vector $same as the vectors, e.g. m or N$
$R_x$: x component of the resultant, sum of the x components of the vectors $same as the vectors, e.g. m or N$
$R_y$: y component of the resultant, sum of the y components of the vectors $same as the vectors, e.g. m or N$

When you use it

Use this after adding vectors by the component method, when you need the size of the resultant vector.

Drafted from Grade 11 Physics, pages 17-46, then checked twice before it went up

Magnitude of a sum is not the sum of magnitudesCommon mistake

When you use it

Use this when you add two vectors that do not point in the same direction and need the magnitude of the resultant.

Watch out

The magnitude of A+B equals |A|+|B| only when the vectors are parallel. A 3 N force and a 4 N force at right angles give a resultant of 5 N, not 7 N.

Drafted from Grade 11 Physics, pages 17-46, then checked twice before it went up

Scalar (dot) product of two vectorsFormula

\vec{A}\cdot\vec{B}=AB\cos\theta=A_xB_x+A_yB_y

\vec{A}\cdot\vec{B}=AB\cos\theta=A_xB_x+A_yB_y

$A$: magnitude of vector A $same as the vector A, e.g. N or m$
$B$: magnitude of vector B $same as the vector B, e.g. N or m$
$\theta$: angle between A and B when placed tail to tail $\degree$

When you use it

Use this to find the angle between two vectors or to calculate work and power from a force and a displacement or velocity.

Watch out

The dot product is a scalar, not a vector, so its answer has no direction. Place the vectors tail to tail before reading the angle.

Drafted from Grade 11 Physics, pages 17-46, then checked twice before it went up

motion in one and two dimensions

Acceleration sign and speeding up or slowing downCommon mistake

When you use it

Use when a question asks whether a moving object is speeding up or slowing down, or when it gives a negative acceleration.

Watch out

A negative acceleration does not always mean slowing down. The object speeds up when velocity and acceleration have the same sign and slows down when they have different signs.

Drafted from Grade 11 Physics, pages 47-94, then checked twice before it went up

Centripetal acceleration in uniform circular motionFormula

a_c = \frac{v^2}{r}

a_c = \frac{v^2}{r}

$a_c$: centripetal acceleration, directed towards the centre $m\,s^{-2}$
$v$: tangential (linear) speed $m\,s^{-1}$
$r$: radius of the circular path $m$

When you use it

Use when an object moves in a circle at constant speed and you need the acceleration towards the centre.

Watch out

Use the radius, which is half the diameter. Convert km/h to m/s by dividing by 3.6 before substituting, for example 50.4 km/h = 14 m/s.

Drafted from Grade 11 Physics, pages 47-94, then checked twice before it went up

Kinematic equations for uniform accelerationReference tablev_f = v_i + at · s = (v_i + v_f)/2 t · s = v_i t + 1/2at^2 · +2

Equation	Missing quantity
$v_f = v_i + at$	$s$
$s = \frac{v_i + v_f}{2}\,t$	$a$
$s = v_i t + \frac{1}{2}at^2$	$v_f$
$s = v_f t - \frac{1}{2}at^2$	$v_i$
$v_f^2 = v_i^2 + 2as$	$t$

When you use it

Use for straight line motion with constant acceleration when displacement, velocity, acceleration or time is needed. Pick the equation that leaves out the quantity you do not need.

Watch out

These equations apply only when acceleration is constant. They do not apply if acceleration changes.

Drafted from Grade 11 Physics, pages 47-94, then checked twice before it went up

Velocity change under constant accelerationFormula

v_f = v_i + at

v_f = v_i + at

$v_f$: final velocity $m\,s^{-1}$
$v_i$: initial velocity $m\,s^{-1}$
$a$: constant acceleration $m\,s^{-2}$
$t$: time interval $s$

When you use it

Use when acceleration is constant and you need the final velocity after a time t.

Watch out

Velocities and acceleration are vectors. Choose one positive direction first and give each quantity its sign before substituting. Use the equation only when acceleration is constant.

Drafted from Grade 11 Physics, pages 47-94, then checked twice before it went up

Dynamics

Action and reaction do not cancelCommon mistake

When you use it

Use this when a question asks for the resultant of an action force and its reaction, or when you add forces to find the net force on one body.

Watch out

Action and reaction are equal and opposite but act on two different bodies, so they cannot be added to give zero. Sum only the forces acting on the same body.

Drafted from Grade 11 Physics, pages 95-174, then checked twice before it went up

Maximum static frictionFormula

F_s \le \mu_s F_N

F_s \le \mu_s F_N

$F_s$: static friction force, which can take any value up to its maximum $N$
$\mu_s$: coefficient of static friction for the two surfaces $dimensionless$
$F_N$: normal force pressing the surfaces together $N$

When you use it

Use this to decide whether a body at rest will stay at rest, or to find the largest friction force before it starts to slide.

Watch out

Static friction is only at most mu_s F_N, not always equal to it. Once the body slides, switch to kinetic friction, F_k = mu_k F_N, which is smaller than the static maximum.

Drafted from Grade 11 Physics, pages 95-174, then checked twice before it went up

Newton's second law: net force and accelerationFormula

F_{\text{net}} = ma

F_{\text{net}} = ma

$F_{\text{net}}$: net force, the vector sum of all forces on the body $N$
$m$: mass of the body $kg$
$a$: acceleration in the direction of the net force $m\,s^{-2}$

When you use it

Use this when a body accelerates under one or more forces and you need either the acceleration or the net force.

Watch out

Use the net force, the vector sum of all forces including friction, not the applied force alone. Example 4.7 subtracts friction before dividing by the total mass.

Drafted from Grade 11 Physics, pages 95-174, then checked twice before it went up

Normal force on an inclineFormula

F_N = mg\cos\theta

F_N = mg\cos\theta

$F_N$: normal force from the slope on the body, perpendicular to the surface $N$
$m$: mass of the body on the slope $kg$
$g$: acceleration due to gravity $m\,s^{-2}$
$\theta$: angle of the incline with the horizontal $^\circ$

When you use it

Use this when a block rests on or slides down a slope at angle theta and you need the surface's push on it, for example before calculating friction.

Watch out

Normal force equals weight only on a level surface. On a slope it is mg cos theta, which is smaller, so friction on the slope must be calculated from this value.

Drafted from Grade 11 Physics, pages 95-174, then checked twice before it went up

Weight of a bodyFormula

W = mg

W = mg

$W$: weight, the gravitational force on the body $N$
$m$: mass of the body $kg$
$g$: acceleration due to gravity at that place, about 9.8 m/s^2 near Earth's surface $m\,s^{-2}$

When you use it

Use this to find the weight of a body near Earth's surface or on another planet or moon.

Watch out

Weight is a force in newtons while mass is in kilograms. The value of g changes from place to place, so the same mass has a different weight on the Moon (g = 1.6 m/s^2 in Example 4.1).

Drafted from Grade 11 Physics, pages 95-174, then checked twice before it went up

Heat Conduction and Calorimetry

Heat balance in a calorimeterFormula

m_s\,c_s\,(T_s - T_f) = m_w\,c_w\,(T_f - T_w) + m_k\,c_k\,(T_f - T_w)

m_s\,c_s\,(T_s - T_f) = m_w\,c_w\,(T_f - T_w) + m_k\,c_k\,(T_f - T_w)

$m_s$: mass of the hot solid sample $kg$
$c_s$: specific heat capacity of the solid (unknown) $J\,kg^{-1}\,K^{-1}$
$T_s$: initial temperature of the solid $°C$
$T_f$: final equilibrium temperature of the mixture $°C$
$m_w$: mass of the water in the calorimeter $kg$
$c_w$: specific heat capacity of water $J\,kg^{-1}\,K^{-1}$
$T_w$: initial temperature of the water and calorimeter $°C$
$m_k$: mass of the calorimeter and stirrer $kg$
$c_k$: specific heat capacity of the calorimeter material $J\,kg^{-1}\,K^{-1}$

When you use it

Use this when a hot solid is placed in water inside a calorimeter, or a heater warms water in a calorimeter, to find an unknown specific heat capacity.

Watch out

Include the calorimeter and stirrer term whenever their mass is given. Drop it only when the question says to neglect the container.

Drafted from Grade 11 Physics, pages 175-216, then checked twice before it went up

Latent heat during a phase changeFormula

Q = m\,L

Q = m\,L

$Q$: heat absorbed or released during the phase change $J$
$m$: mass of the substance changing phase $kg$
$L$: latent heat: L_f for fusion or L_v for vaporization $J\,kg^{-1}$

When you use it

Use this when a substance melts, freezes, boils or condenses at its fixed transition temperature, such as ice melting at 0 °C or water boiling at 100 °C.

Watch out

The temperature stays constant during a phase change, so do not use mcΔT for that stage. For ice heated from -50 °C, treat heating, melting and heating again as separate steps.

Drafted from Grade 11 Physics, pages 175-216, then checked twice before it went up

Linear thermal expansionFormula

\Delta L = L_0\,\alpha\,\Delta T

\Delta L = L_0\,\alpha\,\Delta T

$\Delta L$: change in length $m$
$L_0$: original length at the initial temperature $m$
$\alpha$: coefficient of linear expansion of the material $K^{-1}$
$\Delta T$: change in temperature $K$

When you use it

Use this when a rod, wire or track changes length because its temperature changes, for example a steel rail on a hot day or a bridge gap.

Watch out

For area use β = 2α and for volume use γ = 3α. Do not use α directly for area or volume expansion.

Drafted from Grade 11 Physics, pages 175-216, then checked twice before it went up

Electrostatics and Electric Circuit

Coulomb's lawFormula

F = k\frac{|q_1 q_2|}{r^2}

F = k\frac{|q_1 q_2|}{r^2}

$F$: magnitude of the electrostatic force between the two point charges $N$
$k$: Coulomb constant, k = 1/(4 pi epsilon_0) = 9.0 x 10^9 $N\,m^2\,C^{-2}$
$q_1, q_2$: the two point charges $C$
$r$: distance between the two charges $m$

When you use it

Use this when you need the electrostatic force between two point charges separated by a distance r.

Watch out

Convert the distance to metres before squaring it. For example 1.0 cm = 0.01 m, so r^2 = 1.0 x 10^-4 m^2, not 1.0. Attraction or repulsion comes from the signs of the charges, not from the formula.

Drafted from Grade 11 Physics, pages 217-286, then checked twice before it went up

Electric field of a point chargeFormula

E = k\frac{Q}{r^2}

E = k\frac{Q}{r^2}

$E$: electric field strength at distance r from the point charge $N\,C^{-1}$
$k$: Coulomb constant $N\,m^2\,C^{-2}$
$Q$: source point charge that produces the field $C$
$r$: distance from the source charge to the point of interest $m$

When you use it

Use this when you need the electric field strength at a point a distance r from a single point charge.

Watch out

The field does not depend on a test charge, so do not multiply by q. For several charges, add the field vectors with their directions, not their magnitudes. Field points away from a positive source and towards a negative source.

Drafted from Grade 11 Physics, pages 217-286, then checked twice before it went up

Ohm's lawFormula

R = \frac{V}{I}

R = \frac{V}{I}

$R$: resistance of the conductor or resistor $\Omega$
$V$: potential difference across the conductor $V$
$I$: current through the conductor $A$

When you use it

Use this to find resistance, voltage or current in a metal conductor when its temperature stays constant.

Watch out

Ohm's law holds only at constant temperature. A filament lamp is non-ohmic: its resistance rises as it heats, so its V-I graph curves rather than being a straight line through the origin.

Drafted from Grade 11 Physics, pages 217-286, then checked twice before it went up

Nuclear Physics

Alpha and beta decay changesReference tableα · β^- · β^+

Decay	Emitted particle	Change in A	Change in Z
$\alpha$	$^{4}_{2}\mathrm{He}$	$-4$	$-2$
$\beta^{-}$	$^{0}_{-1}\mathrm{e}$	$0$	$+1$
$\beta^{+}$	$^{0}_{+1}\mathrm{e}$	$0$	$-1$

When you use it

Use when you must write a decay equation or find the daughter nucleus from a parent nucleus.

Watch out

Beta minus raises Z by one and leaves A unchanged, because a neutron becomes a proton and an electron. Beta plus lowers Z by one. Do not change A in any beta decay.

Drafted from Grade 11 Physics, page 287 onwards, then checked twice before it went up

Binding energy per nucleon divides by ACommon mistake

When you use it

Use when a question asks for the binding energy per nucleon, after you have found the total binding energy of the nucleus.

Watch out

Divide by the mass number A, the number of nucleons, not by the atomic number Z. For oxygen-16 divide by 16, not 8. Example 7.2 divides 118.808 MeV by 16.

Drafted from Grade 11 Physics, page 287 onwards, then checked twice before it went up

Radioactive decay law and half-lifeFormula

N=N_0 e^{-\lambda t}

N=N_0 e^{-\lambda t}

$N$: number of undecayed nuclei at time t $1$
$N_0$: number of undecayed nuclei at time t = 0 $1$
$\lambda$: decay constant, probability of decay per unit time $\mathrm{s}^{-1}$
$t$: elapsed time $\mathrm{s}$

When you use it

Use when a question gives the initial number of undecayed nuclei and a decay constant or half-life, and asks how many remain after a time t.

Watch out

Lambda is in s^-1, so t must be in seconds; convert years to seconds first. The half-life is t_{1/2} = 0.693/lambda. It is the time for half the nuclei to decay, not the lifetime of the nucleus.

Drafted from Grade 11 Physics, page 287 onwards, then checked twice before it went up

The Grade 11 Physics textbook

The student textbook for the new curriculum, free as a PDF. The cards on this page follow its chapters.

Ministry of Education edition, English
338 pages
Download the PDF

What the book covers

1.Physics and Human Society
2.Vectors
3.motion in one and two dimensions
4.Dynamics
5.Heat Conduction and Calorimetry
6.Electrostatics and Electric Circuit
7.Nuclear Physics

The same subject in other years

An exam paper keeps asking for what the year below taught. Those cards are here too.

Your other Grade 11 subjects

Everything else in this year that has cards so far.

Questions students ask

What do the Grade 11 Physics cards cover?: 36 cards across 7 chapters of the national textbook: Physics and Human Society, Vectors, motion in one and two dimensions, Dynamics, Heat Conduction and Calorimetry, Electrostatics and Electric Circuit and Nuclear Physics. You can take any chapter one card at a time on the page itself.
Is there a national exam in Grade 11?: No. Ethiopia sets national exams in Grade 6, Grade 8 and Grade 12 only. These cards are for your school's own exams, and for the national exam that comes a few years later.
Where do these cards come from?: They are drafted from Grade 11 Physics, the Ministry of Education textbook for this grade. A second pass that cannot see the chapter then re-derives every formula, constant and table row, and anything it cannot confirm is held back instead of published.
Is this free?: Yes. Every card here is free to read and the printable sheet is free to download. Neither needs an account.
When was this last checked?: 12 October 2026. Cards arrive chapter by chapter, and the line under each one says when that card was last read through.

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