P5 Revision
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  • 1. Written by MJ BradleyP5 SPACE FOR REFLECTION incident ray i i-angle of incidence air Refraction The critical angle 1 glass refracted ray When light passes 2 Light refracts (bends) when it enters a substance of differ- form a more dense ent density because it changes speed. Refractive index is substance to a less glass a measure of how much a substance bends light r r-angle of refraction dense substance there is a critical 2 Calculating refractive index (n):n = light speed in vacuum n = sin i angle (c) where the 1 c Dispersion of emerging ray light speed in substance sin r Light In a grazes the bound- At angles of incidence prism light is ary surface greater than the critical Question : What is the refractive index of glass for light at an incident angle dispersed into angle TIR occurs of 30o which refracts with an angle of refraction equal to 20o? different col- ours because The Endoscope Answer: n = sin i/sinr = sin30/sin20 = 0.5/0.34 = 1.47 each colour (or frequency) is In an endoscope some opti- refracted differ- cal fibres totally internally How Optical Fibre works entlyTotal Internal Reflection reflect light down towards less dense layer the stomach (in this exam- cats-eye. Light is ple) and other optical fibres i internally reflected inside dense the glass prism i take the reflected light from Violet is the stomach back to be TIR occurs when the refracted the incident ray is at an angle, i, most and red viewed by a camera and greater than the critical The light totally internally reflects at the the least screen angle inside a dense boundary of the two layers. i must be material greater than the critical angle Convex lens: these refract light rays inwards Optical fibre and Communications Digital signals (on and off) can be transmitted using Fibre optic cable optical fibre. Infra-red pulses in digital code are totally internally reflected along the fibre principal axis C f Light is internally reflected down the cable. Endoscopes Diffraction: This is the spread- f use fibre optic cable The fatter the ing out of waves when they pass lens the shorter through a gap or pass an object. the focal lengthWave revision: The effect is greatest when the The greater wavelength equal the gap width the ampli- Principal focus: rays parallel to the principal wavelength amplitude tude the brighter axis are refracted towards the principal focus (f). the light The distance cf is the lens FOCAL LENGTH or the louder the Images from a convex lens sound Rule1: A ray parallel to the principal axis is refracted through the principal focus FInterference: Waves can interfere with each other constructively Rule 2: A ray through the optical centre does not change direction.(add) or destructively (cancel each other out) peaks and The peaks of tree lens troughs one wave add F F match to the troughs of the other 2F image of tree the image is upside down and smaller,It is a REAL image - it can be destructive interference projected onto a screen constructive interference tree An Interference Experiment F F The sound from B quiet 2F the image isWaves can interfere with each other has travelled 1/2 a u p s i d eto produce patterns as shown exam- wavelength further loud down and isples are light, sound and microwaves than from A. Peaks magnified match with troughs quiet The image is now and destructive inter- the correct way up It is a real ference occurs loud and magnified. The image A eye traces back quiet The sound from A where the rays loudspeaker and B has travelled seem to have come A magnifying glass! loud the same distance. from. It is not a real loudspeaker Peaks match with image we call it a quiet peaks and con- virtual image Other loud areas are heard structive interfer- 2F F F because the path differ- loud ence occurs B ence between the two Magnification waves is a whole number quiet of wavelengths. Peaks magnification = height of image match with peaks and con- structive interference oc- loud height of object curs. Why are other quiet A lens Camera quiet eye lens Projector film - not digital! convex lens bulbtree The lens can move forwards or backwards The lens is moved in screen to make a sharp focus. The closer the ob- or out to focus the ject the further the lens must be pulled image on the screen outwards slide
  • 2. Displacement(s) and Velocity(v) Acceleration Scalar and Vector Quantities Displacement is distance in a given direction. acceleration = velocity change, a = v-u v-u Velocity = displacement (m) v = s/t (m/s2) time (s) t a t A scalar quantity has only size. (m/s) time (s) v = final velocity, u = initial velocity, t = time A vector has size and direction Vector addition Example what is the acceleration of a car if scalar vector it accelerates from 10m/s to 20m/s in 2s? 1)Vectors in the same direction add distance displacement 2) Vectors in opposite directions subtract u=10m/s, v=20m/s, t =2s, a=? 2 3) For vectors at right angles use pythagorous a = (v-u)/t = (20-10)/2 =10/2 = 5m/s speed velocity theorem to work out the resultant temperature force 10N 10N √(10 2 +10 2 )= Equations of Motion for an Object with 10N √200=14.3Ν constant acceleration 10N mass acceleration 10N resultant = 10-10 resultant = 10+10 10N v = u + at = 0N 1) Write down data energy momentum = 20N 10N 10N v2 = u2 + 2as 2) Select the appropriate s = ut + 1/2at2 equation Momentum: Objects with large mass and velocity have a big momentum momentum = mass x velocity Example: A rocket accelerates at 1000m/s2 for p 20s. What distance is travelled? (kgm/s) ( kg) (m/s) m v a = 1000m/s2, t = 20s, s=? p = mv s = ut + 1/2at2 = 1000x20 + 0.5x1000x202 Example: What is the momentum of a 200000kg train travelling at 20m/s? = 20000 +200000 = 220000m Answer: p = mv = 200000x20 = 4000000kgm/s Force and Momentum:When momentum changes there is a resultant Projectiles: An object fired horizontally will force. The bigger the rate of change of momentum the bigger the force move at steady speed horizontally (ignoring air resistance) but will accelerate downwards F = rate of change of momentum Force in collisions. To reduce the force because of gravity F(N) = mv - mu (same as F = ma) momentum needs to reduce more slowly i.e. make the time for collision longer using vh vh t(s) vh crumple zones or airbags vv vv vv vhMomentum and collisions: Momentum before = momentum after. This is a very important physics law Projectiles take a parabolic shape through the air vhExample A 1000kg car travelling at 20m/s hits a stationary 20000kg lorry. (a) What is the vvmomentum of the car before impact? Answer :Momentum before = mbvb=1000x20 = 20000kgm/s To answer questions about projectiles(b)If they stick together what is their velocity after the impact? vv use v h=s h/t for the horizontal motionAnswer: Momentum before = momentum after so mbvb = mava (steady velocity horizontally)20000 = (1000+20000)Va Use sd = udt + 1/2at2 or vd2 = ud2 + 2asd for20000 = 21000Va so Va = 20000/21000 = 0.8m/s the downwards motion Newtons III Law When walking your foot pushes back on the road and the road pushes with an equal and When two bodies interact opposite forwards force which causes you to accelerate forwards. The Earth beneath you they exert equal and oppo- also accelerates backwards but you do not notice it because the Earth is so massive site forces on each other Microwave and Radiowave Communications Satellites Microwave Microwave communications must Man made satellites be in line of sight. Microwaves are Medium wave- i on can be used for com- satellite transmitted to a satellite and are re- lengths (around osp her munications, receiver satellite transmitted back to another location 300m) reflect from e weather forecasting, the ionosphere) defence, surveying. transmitter on the Earth. Medium radio wave- ground lengths are reflected from the iono- Geostationary station sphere back to the Earths surface. Orbits transmitter This however is unpredictable and is affected by the sun. Long wave- Satellites near to the lengths can be diffracted around the earth orbit quickly Earths surface. Microwaves Long wave radio because gravity is (wavelength (wavelengths strong. ground station around 1m) 1km) will diffract receiver must be in line At a certain distance of sight around the satellites orbit at the Earths surface same rate as the Diffraction and communications Earth spins and seem Diffraction is the bending of stationary in the sky. waves around obstacles or cor- Satellite Orbits and Centripetal Force They are in a ners. In radio communications geostationary orbit - longer wavelengths diffract the very useful for most. This house will not receive Diffraction can cause some communications short wavelength signals because signal loss at the edge of the F they do not diffract around the hill transmission dish earth comets are natural satellites of the sun as A satellite would rather travel in a straight line if it could! they approach the sun they accelerate be- Gravity is the centripetal(central) force, F which pulls them sun cause gravity is stronger. The tail forms because the icy surface evaporates round in an ellipse shape we call an orbit The moon orbits the earth in the same way and the Earth around the Sun
  • 3. FOLD ALONG LINE WRITTEN BY MJ BRADLEYRevision Exercise Unit P5 1) slows1) When light passes into a more dense substance it ________ down 2) n = sin i n = speed of light in vacuum2) Two equations for refractive index are.......................... sin r speed of light in substance3) Label this diagram with i for the angle of air iincidence, r for the angle of refraction air glass glass3b) Light enters the glass at an angle of incidence equal to 30o. The n = sin i = sin 30 = 0.5 = rangle of refraction is 20o. What is the refractive index of the glass? sin r sin 204) Total internal reflection can only occur at a ________ dense to _____ 4) more, less, criticaldense boundary and when the angle of incidence is greater than the_________ angle 5) refraction, least, violet5) White light shone into a glass prism is dispersed into different coloursbecause the amount of ________ is different for each colour. Red isrefracted the _______ and ________ the most.6) Complete the paths of these light rays as 6)+6b)they emerge from a convex lens F6b) Label the principle focus F 7) Draw two rays from the top of the tree and show where its image will be formed 7 lens lens F F tree F F 2F 2F 7b) Describe how the image is different to the object 7b) upside down and smaller 8) Draw two rays from the top of the pencil and show where its image will be formed 8) pencil F pencil 2F F F F 2F 9) Trace back the paths of these rays and show where the top of the 9)+9b) magnifying glass pencil image will seem to be9b) What type of optical instrument could this be? 2F F F9c) Magnification = ?/? 9c) = image height 2F F F object height10) In a camera and projector how is the image focused? 10) By moving the convex lens in or out11) Constructive interference between two waves occurs 11) peaks match with peakswhen......................................... eye12) Destructive interference between two waves occurswhen......................................... eye 12) peaks match with troughs13) If the path difference between two waves is a whole 13) constructivenumber of wavelengths _________ interference will occur14) If the path difference between two waves is any 14) destructivenumber of half wavelengths _________ interference oc-curs15)Write the following data down using the correct symbols: t, v, u, S, a 15) t = 5s, v = 30m/s, u = 20m/s, S = 125m, a = 2m/s2A car travelling at 20 m/s accelerates to 30m/s in 5s. The acceleration of thecar is 2m/s2 and the displacement is 125m16) A man walks 100m east then 25m 16a) d = 100 + 25 = 125mnorth 25m start(a) What is the total distance walked?(b) What is the displacement from the 100m (b) displacement S = √(1002 + 252) =start?17) All vector quantities have size and _______________ 17) direction18) Scaler quantities have _________ only 18) size19) A stone is dropped from rest and falls for 3s. Use s =ut + at2/2 to find 19) s =ut + at2/2 = 0x3 + 10x32/2out how far it will fall in 3s (Acceleration due to gravity = 10m/s2) = 0 + 10x9/2 = 45m
  • 4. WRITTEN BY MJ BRADLEY Revision Exercise Unit P5 FOLD ALONG LINE 20)20) A stone is thrown horizontally with a velocity of 20m/s at a height of 1.5m (a) parabolic(a) What shape describes the path the stone will take (b) constant(b) What can you say about the horizontal velocity of the stone? (c) zero(c) What is the initial velocity vertically? (d) s =ut + at2/2(d) Use s =ut + at2/2 to work out the time it takes for the stone to hit theground (acceleration due to gravity = 10m/s2) 1.5=0xt+10t2/2 = 5t2 so t2 = √(1.5/5) =(e) How far will the stone travel horizontally before hitting the ground?21) A car must stop form a speed of 50 m/s in 20m, what is the deceleration? 21) s = v2 - u2 = 02-502 = 0 - 2500 = -2500 = -25 m/s2(Clue use v2=u2 + 2as) 2s 2x50 100 10022) Momentum = ___________ x ____________ or P =mv 22) mass x velocity23) The unit of mass is kg, the unit of velocity is _____, the unit of momentum is 23) m/s, kgm/s_________24) The momentum before a collision = ________________________ 24) momentum after collision25) What is the momentum of a 1000Kg car travelling at 10m/s? 25) p = mv = 1000x10 = 10000kgm/s25b) The car collides with a stationary 10000kg bus and they stick together. What 25b) 10000kgm/smust be their combined momentum after the collision? b(ii) 10000 = (10000+1000)vb(ii) What velocity do they have? so 11000v = 10000 v = 10000/11000 v=26) In a collision the forces are large if momentum changes very ________ 26) quickly27) force = change in momentum, in symbols F = ? - ? 27) change in momentum, in symbols F = mv - mu ? ? time t28) A 1000kg car has a velocity of 50m/s. It hits a bridge and stops in 0.5s. 28)(i) What is the momentum before hitting the bridge? (i) P = mu = 1000 x 50 = 50000 kgm/s(ii) What is the momentum of the car only after the collision? (ii) P = mv = 1000 x 0 = 0(iii) What is the change in momentum? (iii) change = mv - mu = -50000kgm/s(iv) What is the force? (iv) F = (mv-mu)/t = -50000/0.5 = 100000N(v) How can the force on the car be reduced? Explain why (v) Use crumple zones - they increase the time for collision28b) When the car hit the bridge the force of the car on the 28b) carbridge was equal and opposite to the force of the bridge onthe............................................29) Diffraction is the ______ of waves obstruction 29) bending, gap, wavelengthas they pass through a ______. Theeffect is greatest when the gap width isequal to the ___________. Wider gapscause little bending wave crests large gap30) Explain why this house can receive long 30) Longer wavelengths are able to diffract around thewave radio but not short wave radio mountain31) In radio communications long waves are able to ____ around theearths surface. Medium waves are able to reflect off the ________. 31) diffract, ionosphere, sight, EarthMicro waves work only by line of _______ and need satellites torelay signals around the ______.32) Three uses of satellites are ................................... 32) communications, defence, weather forecasting33) Satellites are kept in orbits by the Earths _______. This is an 33) gravity, centripetal, straightexample of a ________ force and without it satellites would continuein a ________ line away from the Earth34) A satellite in a geostationary orbit moves at the same rate as the 34) spins on its axisEarth _______. 35) natural, gravity gets stronger35) Comets are _________ satellites of the Sun. As they approach theSun they speed up because...........
  • 5. PHYSICS ASSESSMENT P5 SPACE FOR REFLECTION Name __________________________________________________ satellite(a) This artificial satellite is in a geostationary orbit. Complete the following sentences about satellites. Choose from height period 24 hours position equator A geostationary stationary satellite orbits the Earth once in________________ It stays in a fixed above the Earth’s surface. The ___________________ above the Earth’s surface determines the orbital ____________ of the satellite. [3] (b) Artificial satellites are used for transmitting information. They use electromagnetic waves to carry the information. Describe how the satellites are used to transmit information. ____________________________________________________________________ _____________________________________________________________________ ____________________________________________________________________[2] (c) Artificial satellites have different uses. Geostationary satellites are used for communica- tion. They have a high orbit. Other satellites have a low polar orbit. State one use for low polar orbit satellites. _______________________________________________[1] (d)Part of the Earth’s upper atmosphere is called the ionosphere. It is used for transmitting information. Explain how radio waves are transmitted around the Earth using the ionosphere. In your answer use your ideas about: •what the ionosphere is •what frequency of radio waves are used •what happens to the waves when they strike the ionosphere.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________[2]2) This question is about the motion of two 15m/scars A and B 10m/s A B (a) (i) The speed of each car is shown. Speed is a scalar quantity. What other piece of information would be needed to describe the car’s velocity? [1] (ii) Velocity is not a scalar quantity. What type of quantity is velocity? _________________[1] (b)(i) Car B accelerates at 2 m/s2 for 3 seconds. Calculate the final speed of car B. ________________________________________________________________________ ____________________________________________________________________[2] (ii) Car B has a mass of 1 500 kg. Calculate the final momentum of car B. ________________________________________________________________ ____________________________________________________________[2 (c) Car A catches up with car B. The driver does not brake quickly enough. The cars collide. Write down two things about the force on the cars at the moment of impact. At the moment of impact the forces exerted by the cars on each other are and [2]
  • 6. 3 (a) A ball is projected horizontally in the Earth’s gravitational field. Ignoring air resistance what happens to the horizontal speed of the ball? Put a ring around the correct answer. ball the speed increases the speed stays the same the speed reduces [1] (b) The ball moves towards the ground. What happens to the vertical speed of the ball? [1] (c) The ball has a resultant velocity. Explain what produces the resultant velocity of the ball. Use your ideas about vectors in your answer. _______________________________________________________________________________ ____________________________________________________________________________[2] 4 This question is about white light entering a glass white light prism. The light refracts and disperses into different red colours violet (a) The amount of bending is different for each of the spectral colours. Complete the following to explain why the amount of bending increases. The amount of bending increases with a greater change of . [1] (b) Red light is deviated less than blue light. Explain why. Use your ideas about refractive index in your answer. _________________________________________________________________________ _____________________________________________________________________________________ ________________________________________________________________________________[2]5 This question is about the interference of waves. AThe diagram shows two sources of light A and B from area where rays overlaptwo slits in a card in front of a lamp B (a) Interference is evidence for the wave nature of light. Name one other piece of evidence. [1] (b) The area where the waves overlap is where an interference pattern is produced. Describe the area of interference pattern and explain how the waves produce it. ___________________________________________________________________________________ _________________________________________________________________________________[2]6 This question is about convex lens principal focuslight through a convex lens axis ray x Ray X is travelling parallel to the axis of the lens. For the first part of this question (a), draw your answers on the diagram above. (a) (i) Complete the path of ray X after it passes through the lens. [1] (ii) Draw the path of one other ray to show where the image of the object is formed. [1] (b) The size of the object is 2 cm. The size of the image produced is 6 cm. Calculate the magnification. [2]