PHYSICS

Question 1

The trajectories of the motion of the golf ball with air resistance and without
air resistance are shown.
Trajectory without
air resistance
Trajectory with
air resistance
Explain the differences between

Answer 1

When moving up weight and (vertical component of) air resistance are
acting.
Or When moving up air resistance increases the resultant force.
* (When moving up,) downwards/vertical acceleration/deceleration increases
Or upward velocity decreases more quickly.
* (So maximum) height is lower.
Horizontal motion
* There is a horizontal deceleration/force (due to air resistance).
* (So the average) horizontal velocity is lower.
* The (ball travels a) shorter (total) distance.

Question 2

‘how to find trminal velocity

Answer 2

ace two or more rubber bands or markers (on the cylinder)
(accept markers correctly placed and labelled on diagram)
The top band should be far enough below the surface for terminal
velocity to have been reached
Or have more than 2 markers and check velocity is constant.
Measure time for the sphere to fall a given distance (using the
stopwatch) and measure distance fallen (using the metre rule)
Either
Reference to repeated measurements and averaging
(terminal velocity =)
distance between markers
(average) time between markers
Or
measure the times for different distances
(terminal velocity =) gradient of graph of distance against time
(1)
(1)
(1)
(1)
(1)
(1)
(

Question 3

why is there maxium velocity of the car

Answer 3

As velocity increases the air resistance increases
(When) frictional forces are equal to the (driving) force of engine/car
There is no resultant/net/unbalanced force and no acceleration

Question 4

State what is meant by plane polarised.

Answer 4

Vibrations/oscillations in one plane
which includes the direction of wave travel

Question 5

Describe how a value for the speed of sound in air can be determined.

Answer 5

Describes an initial situation where the two traces are in antiphase / phase
Record the position of the microphone (from the metre rule)
Or Measure the distance from the loudspeaker to the microphone
Move microphone (gradually) until the two traces are next in antiphase / phase
Record the new position of the microphone and calculate the distance moved
by the microphone
Or Measure the new distance from the loudspeaker to the microphone and
calculate the distance moved by the microphone
Multiply calculated/measured wavelength by frequency to determine the speed
Or Describes a suitable graph to determine the speed

Question 6

) Explain why the polarimeter light source should have a low power.

Answer 6

Higher power lamp would have a heating effect on the solution
Or Higher power lamp would increase the temperature of the solution
* Heating would cause expansion of the sucrose solution
Or heating would cause evaporation of the sucrose solution
* Which would change the concentration/density (of sucrose solution)

Question 7

Suggest two modifications that would improve the accuracy of the value of the Planck
constant determined from this experiment.

Answer 7

Block out external light sources
* Use a larger range of wavelengths/frequencies
* Use filters with a narrower frequency band
* Use LEDs of known frequency
* Use more sensitive ammeter

Question 8

Explain whether the term ‘free fall’ is

Answer 8

Free fall means that weight/gravity is the only force acting on the
object/probe

Question 9

) Explain why the mass of the athlete has little effect on the initial acceleration.

Answer 9

Initially friction/drag negligible/small/less (as the velocity is low)
* See mgsin Or Wsin
* mgsin = ma and the masses cancel (so a independent of m)

Question 10

Explain why the sample of wire used in this experiment should be long and thin

Answer 10

• For long(er) wire, the extension will be large(r)
• (For the same load) extension is proportional to the original length
  Or extension
  original length = constant
• For a thin(ner) wire, the extension will be large(r)
• (For the same load) extension is inversely proportional to cross-sectional area
  (may be explained in terms of E ,  and ε)
• The percentage uncertainty in the extension/length will be lower (although
  this will be greater for the cross-sectional area)
• A small(er) load can be used with a long/thin wire

Question 11

drift velocity

Answer 11

The average/mean velocity of the (free) electrons
(allow “speed” for “velocity”, and “charge carriers” for “electrons”).

Question 12

As the light intensity incident upon the LDR decreases, the power dissipated in
the fixed resistor decreases.
Explain why the power in the fixed resistor decreases.

Answer 12

Decrease in the number of conduction/ free electrons
Greater resistance of LDR
Less p.d. across the fixed resistor
(allow “voltage” for “p.d.”)
Use of a suitable power equation to conclude that less power dissipated
in the fixed resistor.
(Converse argument not allowed for MP1 & MP2)

Question 13

Describe the process by which visible light is emitted from the sodium atoms

Answer 13

(Sodium) electrons/atoms gain/absorb energy
And electrons move to higher energy levels
(Sodium) electrons drop to lower energy levels, releasing photons

Question 14

LOUD SOUND

Answer 14

Path difference is zero
Or both waves have travelled the same distance from the speakers to O
Waves are in phase
Constructive interference/superposition takes place

Question 15

) State the conditions required for total internal reflection to occur.

Answer 15

For light travelling in a more (optically) dense substance and meeting a
less (optically) dense substance
Or for light travelling a material with higher RI and meeting one with a
lower RI
Angle of incidence is greater than (or equal to) the critical angle

Question 16

Explain which, if either, of the two arrangements would lead to a greater value for the
terminal potential difference.

Answer 16

n series/A there is a greater (combined) resistance than in parallel/B
Or Resistance in series/A is 2R, resistance in parallel/B is R/2.
So greater current in parallel/B Or so less current in series/A
As ε and r the same Or since ε = V + Ir Or more lost volts in parallel/B
Terminal potential difference is greater in series/A

Question 17

Explain how the diffraction pattern provides evidence for the wave nature of electrons.
(

Answer 17

• (Diffracted) electrons experience (constructive) interference/superposition
  Or the pattern is evidence electrons have interfered/superposed
• Diffraction/interference is a wave property

Question 18

stationary waves uncertainty and how to fix it

Answer 18

Frequency
* Uncertainty in identifying when nodes form
* Uncertainty in identifying maximum amplitude
Length
* Parallax error when measuring length
* Uncertainty in measuring length to top of pulley
Or uncertainty in measuring length as string is not straight
Mass
* Zero error on mass balanceFrequency
* Repeat and calculate the mean frequency
* Vary frequency from above and below resonance to find two values for the
frequency when the standing wave forms
Length
* Use a set square to reduce parallax error in length
Or hold ruler in contact with the wire to reduce parallax error in length
Or ensure ruler and string are at eye-level
* Switch off vibrator
Or ensure string is straight
Mass
* Zero balance before each measurement
* To remove systematic error
Or idea that this error is not reduced by repeating

Question 19

Explain why sand storms reduce the power generated by the solar panels.

Answer 19

Sand(storms) reduce amount/intensity/energy/power of light
Fewer electrons released in the (solar) panel
Sand(storms) absorbs/blocks/reflects some light
Sand(storms) reduces area of panel/desert

Question 20

Explain how the ultrasound scan of the unborn baby is produced.

Answer 20

Ultrasound is reflected from boundaries/baby
* (This reflection is caused by) change in density
* Time taken between pulse being sent and received measured
* Speed of ultrasound is known
* Speed = distance/time can be used (to calculate the distance to
boundary)
* Clear indication that this calculation includes ½ time or ½
distance

Question 21

work function of a metal.

Answer 21

Minimum energy required to release/emit a (photo)electron (from the
surface of the metal)

Question 22

This photocell works with ultraviolet light but does not work with visible light.
Explain wh

Answer 22

Ultraviolet has a higher (photon) energy (than visible light)
Ultraviolet (photons) have an energy greater than the work function
Or Visible light (photons) have an energy less than the work function

Question 23

The intensity of the ultraviolet light was then increased without changing the
frequency.
Explain what happened to the reading on the ammeter.

Answer 23

(Increased intensity means) more photons per second
(More photons leads to) more electrons emitted (per second)
Reading on ammeter is increased
Or Current is increased

Question 24

Explain why the wave is refracted as shown, as it travels from deep water into
shallow water.

Answer 24

There is a decrease in speed/velocity
Part of the wavefront meets the boundary before the rest

Question 25

Explain, using Huygens’ construction, how diffraction occurs as waves pass through a gap.

Answer 25

Waves spread out (as they pass through the gap) Each point on the wave(front) acts as a source of new/secondary wave(let)s

Question 26

State what is meant by e.m.f.

Answer 26

Energy (supplied) to/per unit charge

Question 27

Explain the process by which nitrogen atoms produce a line spectrum

Answer 27

Energy levels (in atoms) are discrete/specific (Energy makes) electrons move up energy levels Or Electrons are excited (Electrons) move back down energy levels, releasing photons Or (Electrons) are de-excited, releasing photons Energy difference (between levels) is proportional to frequency of photon (resulting in line spectrum being produced) Or Photon energy is proportional to frequency (resulting in line spectrum being produced)

Question 28

i) State why the line spectrum produced by oxygen atoms in the air would be different from the line spectrum produced by nitrogen atoms.

Answer 28

Different atoms/elements have different (differences in) energy levels

Answer 29

Risk of scalding from hot water * Clamp beaker * Risk of burns from hot apparatus * Wear gloves * Risk of electric shock from power supply * Keep separate from water bath Or Use a low voltage power supply

Question 30

Explain two reasons for the lower voltmeter reading.

Answer 30

look in tab

Question 31

xplain, in terms of particles, why the resistance of a filament lamp increases as the potential difference across the filament increases.

Answer 31

As p.d increases, current increases (As current increases,) temperature increases (allow “heats up”) Atoms/ions/lattice have greater vibrations/KE Increased rate of collisions between electrons and atoms/ions

Question 32

Explain how this would affect the value of the Planck constant calculated.

Answer 32

There would be an uncertainty in wavelength/frequency Or there would be a range of wavelengths/frequencies Or the LED emits different wavelengths/frequencies * If wavelength was longer, the calculated Planck constant would be larger

Question 33

Explain the shape of each graph.

Answer 33

For filament bulb, resistance increases (as p.d. increases) Or For filament bulb, p.d. increases at a greater rate than current Or rate of increase of current decreases. * Increased temperature leads to increased vibration of ions/atoms/lattice * Increased rate of collision between electrons and ions/atoms/lattice * For a thermistor, resistance decreases (as p.d. increases) Or For a thermistor, current increases at a greater rate than p.d. Or rate of increase of current increases * Increased number of conduction electrons * I = nAqv, so current increases.

Question 34

) A student suggests that if the wavelength and intensity of the light used are both increased, the maximum speed of the electrons released from the metal surface also increases. Explain whether the student’s suggestion is correc

Answer 34

Increasing intensity leads to more photons/electrons But intensity does not affect the speed/ KE (of electrons) Increasing λ leads to a decrease in photon/light energy Leads to decrease in speed/ KE (for electrons), so student incorrect

Question 35

Explain how the teacher, using the same laser pointer, could improve his value for the number of lines per millimetre.

Answer 35

Measuring distance from from first order maxima on one side of the central maxima to the first order maxima on the other side Increasing distance from diffraction grating to screen It would decrease percentage uncertainty

Question 36

Discuss the advantages of choosing the digital multimeter to measure the potential difference

Answer 36

* (Percentage) uncertainty will be reduced * The multimeter screen/display will not cause a parallax error * The multimeter can measure to a higher resolution Or the multimeter resolution can be increased by changing the setting Or the multimeter measures to 2 d.p. * The digital multimeter will not require interpolation of values

Answer 37

Take a resistance measurement at 0 ˚C * to measure R0 accurately * Take resistance measurements for lower temperatures * to improve the accuracy of the gradient Or to improve the accuracy of the y-axis intercept * Take resistance measurements for smaller increments of temperature * to improve the accuracy of the gradient Or to improve the accuracy of the y-axis intercept * Take resistance measurements for a wider range of temperatures * to improve the accuracy of the gradient Or to improve the accuracy of the y-axis intercept * Stir the water regularly Or place the thermometer inside the copper coil * so the temperature of water plotted is the same as the temperature of the copper * Use a datalogger to measure temperature and resistance * so that the values are recorded simultaneously * Use a digital thermometer * to avoid parallax error

Question 38

Explain what is meant by terminal velocity

Answer 38

The constant maximum velocity reached by an object falling (through a fluid) When the resultant force equals zero Or when the drag plus the upthrust eq

Question 39

) Explain the difference between unpolarised and plane polarised light.

Answer 39

Unpolarised light vibrates/oscillates in all planes Plane polarised light vibrates/oscillates in one plane Including the direction of wave travel

Question 40

PD

Answer 40

Potential difference is the energy transfer per unit charge

Question 41

Explain the process that results in the emission of different wavelengths of visible light

Answer 41

Atoms/electrons absorb energy/photons * Electrons move to higher energy levels * Then drop down energy levels, releasing photons * Energy levels are discrete * For hydrogen atoms, there are only a small number of possible energy level differences (that can occur to produce visible light) * Since E = hf and v = fλ, only certain wavelengths are emitt

Answer 42

Take readings for p.d. and current Change resistance / R Plot a graph of V against I Gradient is −r

Question 43

Explain why the maximum kinetic energy of a released electron is less than the energy of each photon of light incident on the surface.

Answer 43

The electron only receives energy from one photon Or there is a one to one interaction between photons and electrons Some of the photon energy is needed to overcome the work function Or There is a minimum energy required to release electrons from the (surface of the) plate Remaining photon energy is transferred to kinetic energy of electron (and is therefore lower than photon energy) Or Photon energy is shared between the work function and kinetic energy of electron (so kinetic energy less than photon energy)

Question 44

Explain how measurements of current and potential difference could be used to demonstrate that charge and energy are both conserved in this circuit

Answer 44

Current is the rate of flow of charge * Current is the same at all points in a series circuit Or current in C = current in cell. * total current going into a junction = total current out of junction Or current in C/cell = current in A + current in B Or current splits (equally) between A and B * p.d. is energy transferred per unit charge * p.d is shared between components in series Or p.d. across C + p.d. across A = e.m.f. of cell Or p.d. across C + p.d. across B = e.m.f. of cell Or p.d. across C + p.d. across A/B combination = e.m.f. of cell * p.d. is the same across components in parallel Or p.d. across A is the same as that across B

Question 45

Explain why the power dissipated by the whole circuit changes as the intensity of the light incident on the LDR increases.

Answer 45

Resistance of LDR decreases * Due to increase in number of (conduction) electrons * So the resistance of circuit decreases Or This results in greater current in circuit/LDR/resistor * e.m.f. of the circuit is the same * And due to P = VI Or P = I 2R Or P = V 2 /R (for whole circuit) * The power dissipated by the circuit increases

Question 46

coherence

Answer 46

Same frequency Constant phase difference/relationship