## Physics Paper 2 Questions and Answers - Mathioya Mock 2021 Exams

INSTRUCTION TO CANDIDATES

• This paper contain two sections; Section I and Section II
• Answer all the questions in section I and II In the spaces provided
• All workings and answers must be written on the question paper in the spaces provided below each question
• Marks may be given for correct working even if the answer is wrong
• Calculators and KNEC Mathematical tables may be used EXCEPT where stated otherwise
• Show all the steps in your calculations, giving your answers at each stage in the spaces below each question

FOR EXAMINER’S USE ONLY

 SECTION QUESTION MAX MARKS CANDIDATE’S SCORE A 1-14 25 B 15 12 16 11 17 10 18 09 19 13 TOTAL 80

## QUESTIONS

SECTION A 25 MKS

1. Figure 1 below shows an ammeter used to measure current flowing through a section of a conductor The student used the upper scale

State the reading from the meter (1mark)
2. Why is it safer to carry explosive fuels in metal cans instead of plastic can? (1mark)
3. What do you understand by rating 9W, 240v indicated on an energy saving electric bulb? (1mark
4.
1. Bulb X lights while bulb Y does not Explain (1mark)
2. Figure 3 shows a force on a conductor carrying current when placed in a magnetic field

State the polarities ends R and T (1mark)
T _____________________________________________________
R _____________________________________________________
5. What property does a fuse wire have that make it suitable for controlling excessive currents in circuits? (1mark)
6.
1. The figure 4 below shows an image formed in a plane mirror

By drawing incident rays for the rays shown, locate the position of the object (2 marks)
2. An object is placed 20cm in front of a convex lens of focal length 15cm State one characteristic of the image formed (1 mark)
7. Figure 6 below shows an arrangement of a cylindrical bar magnet suspended freely close and parallel to a fixed solenoid

Explain what motion you are likely to observe in the arrangement when switch K is closed (1mark)
8. A coin is placed at the bottom of a beaker filled with water to a height of 24cm as shown in the figure 7 below Given that the refractive index of water is 133, determine the vertical displacement of the coin (2 marks)
9.
1. The figure 8 below shows an image I formed by an object placed in front of a convex mirror C and F are the centre of curvature and principal focus of the mirror respectively Using appropriate rays locate the object position (2 marks)
2. State one difference between sound waves and electromagnetic waves (1mark)
10.
1. The fig 4 below shows a section of a circuit in domestic wiring

Identify one defect in the wiring (1mark)
2. State one danger of high voltage transmission of electricity over long distances (1mark)
11. Radium  disintegrates into a new stable element lead  how many alpha and Beta particles are emitted (2marks)
12. The figure 2 below shows an electroscope being charged by induction

1. State the reason why the cap of the electroscope is made circular(1 mark)
2. On the same diagram, show the direction of the flow of electrons on the earth wire (1mark)
13. An electric heater is found to have a resistance of 950Ω when operating normally on a 240V mains Find the power of the heater (2marks)
14.
1. The figure below shows a set up by a student investigating propagation of sound waves

Explain what happens to the sound from the bell as the bottle and its contents are cooled to 0°C (1mark)
2. In determining the depth of an ocean an echo sounder produces ultrasonic sound Give one reason why this sound is preferred (1mark)

SECTION B (55 marks)

1.
1. The figure below shows wave fronts approaching the boundary between two media

The speed of the wave in medium (1) is higher than in medium (2) On the same diagram complete the figure to show the wave fronts after crossing the boundaries (1mark)
2. A ray of light is incident on a glass-water interface as shown in figure 11 below

Calculate the angle of incidence i (Take the refractive index of glass and water 3/2 and 4/3 respectively (3 marks)
3. Prisms are preferred to plane mirrors for use in periscopes State one reason for this (1 mark
4. The figure below shows a standing wave on a string of length 27cm

Determine the wavelength of the wave (3 marks)
5. The figure below shows a longitudinal wave that takes 032s to move from point X to Y and at a speed of 50m/s

Calculate
1. the frequency of the wave (2marks)
2. the wavelength of the wave (2marks)
2.
1. State one advantage of an alkaline accumulator over lead acid accumulator (1 mark)
2. Figure below shows resistors in a circuit

Calculate Current through the 4  resistor (3 marks)
3. The graph below shows the Voltage current relationship for a certain battery

Determine:
1. The emf of the cell (1mark)
2. The internal resistance of the cell (3marks)
4. Two coils T and S are wound on a soft iron core as shown T has 1000 turns while S has 600 turns and resistance of 100Ω

Calculate the maximum current measured by the ammeter (3marks)
3.
1. The fig shows as simple form of cathode ray tube, which produces a sharp shadow of a Maltese cross on a fluorescent screen

1. Explain what is meant by cathode rays (1mark)
2. What property of cathode rays does the fig above illustrate (1mark)
2. State one factor that affects photoelectric emission from a given metal surface (1mark)
3. A graph of KE of photoelectrons emitted by metal surface A against the frequency of radiation used is as shown below

From the graph;
1. What is the significance of the gradient of the graph? (1mark)
2. What is the significance of OX (1mark)
4. The threshold frequency for potassium is 537 x 1014Hz When the surface of potassium is illuminated by incident radiation from a source, photoelectrons are emitted with the speed of 79 x105m/s Given that h=662 x 10-34 JS and me=9 x 10-31kg, calculate:
1. The work function for potassium (2marks)
2. The frequency of the incident radiation from the second source (3marks)
4. Figure below shows the features of an X-ray tube

1. Name the parts marked with letters A and H (2marks)
2. Why is tungsten or Molybdenum metal most suitable materials for making part C (1mark)
3. Why is part B made of thick copper metal (1mark)
4. Why should the machine should be surrounded by material G? (1mark)
5. Why is the tube evacuated? (1mark)
6. What effect will increasing current at F have on x-ray produced? (1mark)
7. What effect will increasing the pd between at B and F have on the x-rays produced (1mark)
8. State one way in which cooling is achieved in this X-ray machine (1mark)
5.
1. State one difference between a capacitor and a cell (1mark)
2. Sketch the electrostatic field pattern due to the arrangement of the charges shown (1mark)
3. The diagram shows a parallel plate capacitor with a dielectric material in between the plate

State how each of the following quantities are affected when the dielectric material is pulled out of the parallel plates
1. The pd across the plates (1mark)
2. The charge on the plates (1mark)
3. The capacitance of the system (1mark)
4. Three capacitors of 15µF, 20 µF and 30 µF are connected in series to pd of 12V Find the total charge stored in the arrangement (3marks)
5. The figure below shows a capacitor C being charged

State what would be observed on the following when the switch is closed:
1. The milliameter (1mark)
2. The voltmeter (1mark)
3. Explain how the capacitor is charged (2marks)
6. On the axis provided, sketch the graph of voltage (V) against time (t) (1mark)

## MARKING SCHEME

 1.0.48A √ 1mark 2. Metal cans discharge the static charges while plastic cans accumulate static charges hence can create explosion √ 1mark 3. This means that the bulb is designed to function at maximum voltage of 240V and its energy consumption is 9W. √ 1mark 4  X is connected to a forward biased diode which makes the junction to become smaller while Y is connected to a Reverse biased diode. Diodes conduct only in forward bias. T= NorthR= South  both correct; √ 1mark   √ 1mark 5.  It has Low melting point i.e it is made of a material with low melting point e.g thin copper wire. √ 1mark 6. Image is: Real Inverted Magnified Formed beyond C √ 1mark  Correct ray √ 1mark  Object Any one √ 1mark 7. The magnet is repelled/the magnet moves away from the solenoid since south and North poles are formed at ends A and B respectively √ 1mark 8.  Refractive index =     real depth                                     apparent depthapparent depth = 2.4 = 1.805 cm                           1.33Vertical displacement  = 2.4 - 1.805 = 0.595 Correct subst. √ 1mark Correct ans. With unit √ 1mark 9.    Ø  Sound waves requires material medium (is a mechanical wave)   while electromagnetic waves don’tØ  Sound waves are longitudinal while electromagnetic waves are transverse in nature √ 1mark both rays (incident and reflected)  √ 1mark  Object position Any one √ 1mark 10.  Ø  Connecting the 30A fuse along the neutral line of the heating element. Ø  There is a risk of fire to nearby structures or vegetation when the cables get too low.Ø  There is a risk of electric shock in case the poles collapse or hang too low.Ø  Harmful effects of electric field. √ 1mark Any one √ 1mark 11.  226=206+4x4x=226-206 4x=20    X=5   86=84+2x-y  86=84+10-y    y=94-86  y=85-alpha particles and 8- beta particles are emitted √ 1mark No. of α-Particles√ 1mark No. of β-Particles(Marks independent) 12. For even distribution of charges Upwards √ 1mark √ 1mark(Allow Upwards along earth wire) 13. P = V²/R. P = 240²/950   = 60.63W √ 1mark Correct subst. √ 1mark Correct ans. With unit 14. Ø The intensity of the sound gradually decreases/sound becomes faint(The temperature of the air inside decreases, energy of the molecules decrease hence the rate of vibration decreases) -Ultrasound penetrates the deepest and-can be easily reflected by tiny grains. √ 1mark(Deny-No sound is heard) Any one √ 1mark 15. a)  √ 1mark( Refraction tied to smaller-wavelength, uniform wave fronts)b) √ 1mark- formula &/or√ 1mark -Correct subst. √ 1mark- Correct ans. with unit 15 (c) Ø    Prisms do not absorb energy from incident radiation Ø    Prism do not produce multiple images Ø    Prism do not tarnish or peel off like mirrors √ 1mark- any one (d) 1.5 λ is proportional to 27.0cm 1λ= xx = 27 x 1         1.5 = 18 cm √ 1mark- proportionality √ 1mark -Correct subst. √ 1mark- Correct ans. with unit e)(i) f=1/T    T = 0.32/4 = 0.08  f = 1/0.08 = 12.5 Hz √ 1mark –T√ 1mark - Correct ans. e)(ii) c=λf λ= c/f = 50/12.5=4m √ 1mark -Correct subst. √ 1mark- Correct ans. 16.  Ø  Large currents can be drawn from them over a short period of time.Ø  They require very little attention to maintain.Ø  They are lighter (more portable) than the Lead – acid accumulators.Ø  They can be kept in a discharged condition for a very long time before the cells are ruined √ 1mark- any one b) resistpors in parallel = 3  x 6  =2Ω                                    3 + 6total resistance  = 4 + 2 = 6Ωtotal current  = total voltage =  3 = 0.5A                    total resistance   6Ωcurrent through the 4 Ω resistor = 0.5A √ 1mark –Total resistance√ 1mark-Subst. for I=V/R√ 1mark- Correct ans. c(i)1.65V √ 1mark- correct value of e.m.f (Allow value indicated on the extrapolated graph) ii)  E = V + IrV= -Ir +E-r = slopeslope = change in voltage =   0.4 - 1.5   = -1.1             change in current    0.31 - 0.03    0.28-r= 3.93 ΩInternal resistance = 3.93 Ω √ √  2marks-slope √ 1mark- relating slope with r and correct value ii √ 1mark- formula &/or√ 1mark -Correct subst. √ 1mark- Correct ans. with unit 17.                    Cathode rays are streams of electrons emitted from the surface of a metal by thermionic emission They travel in straight lines(Other property)   They cause fluorescent surfaces to glow                       Intensity of radiation Energy of radiation Type of metal                       The slope represents the value of the Planck’s constant h The region OX represents the value of Work function Wo in Joules                   Wo = hfo= 6.62 x 10-34 x 5.37 x 1014= 3.55 x 10-59J K.E = ½ mev2= ½ x 9 x 10-31 x (7.9 X 105)2= 2.808 x 10-19Jhf = Wo + K.E √ 1mark-√ 1mark-√ 1mark- Any one √ 1mark-√ 1mark-√ 1mark -Correct subst. √ 1mark- Correct ans. with unit √ 1mark –K.E√ 1mark –Subst. in Einstein’s equation √ 1mark- Correct ans. 18 A. Cooling fins        H. Cathode Tungsten or molybdenum has high melting point to withstand high temperatures. To ensure efficient dissipation of heat. To absorb the stray x-ray radiations which would otherwise affect the x ray tube operators To prevent electrons from losing energy due to collisions with air molecules and ionization. The temperature of the cathode increases. This increases the number of electrons released hence the intensity of x-rays. Hard x-rays of very short wavelengths are produced. By efficient cooling fins on the outside of the tube.By circulating oil through the channels in the copper anode. √ 1mark-√ 1mark- √ 1mark-√ 1mark- √ 1mark- √ 1mark- √ 1mark- √ 1mark- √ 1mark- 19  Ø  Capacitor stores electric charge while cell as a device to convert chemical energy to electrical energy.Ø  Capacitor is passive component of circuit while cell is an active component of circuit.Ø  Capacitor discharges instantly while cell runs for longer time.                 P.d increases. Charge remains unchanged. Capacitance decreases.                   Milliameter reading which is initially high gradually reduces to zero. Voltmeter reading increases from zero to maximum value (4.5V). Ø   Negative charges flow from negative terminal of the battery to the plate connected to it.Ø At the same rate, negative charges flow from the other plate of the capacitor towards the positive terminal of the battery.Ø  Equal positive and negative charges appear on the plates.Ø  A potential difference is therefore set on the plates. √ 1mark- Any one√ 1mark- (Direction tied to shape of the field lines)√ 1mark-√ 1mark-√ 1mark- √ 1mark-Capacitance √ 1mark -Correct subst. Q=CV√ 1mark- Correct ans. √ 1mark – √ 1mark –√ 1mark√ 1mark c) √ 1mark- Smooth curve flattening for max. voltage

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