KCSE Past Papers 2019 Physics Paper 2 (232/2)

Questions and Answers

2019 Physics paper 2

1. Figure 1 shows two plane mirrors inclined at an angle of 120° to each other.

A ray of light makes an angle or 40° with the first mirror.

By completing the ray diagram determine the angle of reflection on the second mirror. (2 marks)

  • Correct reflections at the two mirrors.
  • Angle of reflection = 70°2. State the reason why an increase in leaf divergence is the only sure way of determining whether an object is negatively charged using a negatively charged electroscope. (l mark)

     

  • An uncharged conductor will also cause a decrease on the divergence of the leaf. OR 
  • Both positively charged conductor and an uncharged body cause a de- crease in divergence.3. State two properties of magnetic field lines around a bar magnet. (2 marks)

     

  • Do not cross one another.
  • They are complete loops.
  • Direction of field is from North to South.
  • They are normal to the surface at the poles.
  • Closer at the poles and further apart away from the poles.4. Figure 2 shows an incomplete circuit for an electromagnet.

(a) Complete the diagram to show how a battery should be connected at A so that the polarities at P and Q are South and North respectively. (1 mark)

  • (b) State two ways in which the strength of the electromagnet in (a) can be increased. (2 marks)

     

  • Increasing the number of turns in the coil.
  • the current (or number of cells).5. In a siren, sound is produced when a jet of air is directed perpendicular to a ring of holes on a rotating wheel.

    Explain the effect on the pitch of sound produced when the speed of rotation of the wheel is increased. (2 marks)

     

  • Increasing speed increases the frequency of the sound causing an increase in the pitch (higher pitch).6. State the reason why the current produced by a simple cell falls rapidly when the cell is being used. (1 mark)

     

  • Polarization occurs.7. Figure 3 shows a cell connected in series with an ammeter, a 2 resistor and a switch.

    A volumeter is connected across the cell

  • With the switch open, the voltmeter reads 1.5 V. Given that the internal resistance of the cell is 0.5 II, determine the ammeter reading when the switch is closed. (3 marks)I=V/R

    = 1.5 /2 + 0.5

    = — 0.6A

    8. State two uses of gamma rays in medicine. (2 marks)

     

  • To sterilize medical equipment
  • To kill cancerous cells and malignant growths in the body.9. Figure 4 shows the input and output signals on a CRO screen when two diodes are used during a full wave rectification.

  • Explain how the two diodes rectify the input signal. (3 marks) 
  • During the first half cycle of the input signal, current flows in the first diode,
  • During the second half cycle of the input signal, current flows in the sec- ond diode, When the currents through the two diodes are combined a fully rectified wave signal is obtained as the output signal.10. State how the intensity of X-rays in an X-ray tube can be increased. (3 marks)

     

  • By increasing the heating current in order to produce more electrons. Increasing the filaments current.
  • Increasing the temperature of the cathode11. Figure 5 shows part of the lighting circuit in a house.

  • State two errors in the wiring circuit. (2 marks) 
  • Fuse in the neutral wire instead of the live wire.
  • Switch to lamp on the neutral Swire instead of live wire.
  • Connection of lamp B on Live wires only.12. Uranium decays as shown below.

    Name the particle X that is emitted during this decay. (1 mark) 

  • Alpha particle.13. State the disadvantage of rising a convex mirror as a driving mirror. (1 mark)

     

  • Shows the object as being further than it actually is.
  • Shows diminished images.14. Figure 6 shows radiation from the sun passing through glass in a greenhouse onto the floor. The floor then emits radiation.

  • State the name of the radiation emitted by the floor. (1 mark) 
  • InfraredSECTION b (55 marks)

    Answer all the questions in this section

    15. (a) On the axes provided, sketch a graph of Capacitance against the area of overlap of the plates of a parallel -plate capacitor.(1 mark)

    (b) (i) Draw a circuit diagram that may be used to investigate the discharging process of a capacitor. (2 marks)

(ii) On the axes provided sketch the graph of potential difference between the plates against time for the discharging process. (1 mark)

Determine the:

(i) effective capacitance (3 marks)

  • (ii) total charge stored (2 marks)Q = CV

    =2.22 x 10-6 x 6

    = 1.332 x 10-5 C

    (iii) potential difference across the 4uF capacitor(2 marks)

    V=Q/C

    =1.33 x 10-5/ 4 x 10-6

    =3.33V

    16. (a) Define the following terms as used in waves (i) Amplitude (1 mark)

     

  • Amplitude is the maximum displacement of a particle from the mean position.(ii) Waves length (1 mark)

     

  • Wavelength is the distance between two successive points in a wave which are in phase. OR 
  • Distance between two successive crests or troughs in a transverse wave/between two successive rarefaction or compressions in a longitudinal wave.(b) Figure 8 shows water waves approaching a straight reflector at a speed of 40cm’.

(i) Draw on the diagram the reflected waves. (2 marks)

(ii) Given that the distance between the source and the reflector is 15 cm determine:

i). The wavelength of the waves (2 marks)

Wavelength = distance/number of waves

= 15/4

= 3.75cm

(ii). The frequency of the waves (2 marks)

=40 /3.75

— 10.67Hz

(c) Figure 9 sows light rays from two coherent sources S1 and S2 falling on a screen.

Dark and bright fringe s are observed between A and B.

  • (i) State how:I. bright fringes are formed (1 mark)

     

  • Due to constructive interferenceII. dark fringes are formed (1 mark)

     

  • Due to destructive interference.(ii) State what is observed when light of a higher frequency is used. (1 mark)

     

  • The fringes get closer OR
  • When the frequency is higher the wavelength reduces hence the fringe separation decreases.
  • More fringes are formed. 17. (a) Figure 10 shows a ray of light travelling from glass to air.

  • Determine the:(i) Critical angle of the glass — air interface ( 1 mark)

     

  • Critical angle = 42° since the angle of refraction is 90°.(ii) Refractive index of glass (1 mark)

    Sin c = 1/n

    n = 1/sin42°

    =1.495

    (b) A piece of metal is embedded at the centre of an ice block 15 cm from the surface of the ice.

    Given that the refractive index of ice is 1.32, determine how far from the surface of the ice block the metal appears to be. (3 marks)

    Refractive index = Real Depth/apparent Depth

    ∴ apparent Depth =15/1.32

    =11.36cm

Complete the ray diagram to show the path of the rays after passing through the lens. (2 marks)

  • (d) (i) State two differences between the human eye and a camera lens. (2 marks) 
  • Eye has a variable focal length while the focal length of camera lens is fixed.
  • Image distance from the lens is almost constant in the eye while in a camera is can be varied.
  • eye lens cannot be zoomed while te camera lens can be zoomed
  • eye lens is muscular while camera lens is glass or transparent plastic.(ii) State the name of the part of the eye that enable the lens to focus images of objects at different distances. (I mark)

     

  • Ciliary muscles18. (a) Describe how a magnet can be demagnetised using the electrical method. (2 marks)

     

  • Place the bar magnet inside a solenoid placed in an East, West direction then pass an alternating current through the solenoid(b) You are provided with two iron bars P and Q .One of the bars is magnetised while the other is not.

    Explain how the magnetised bar can be identified without using a magnet or magnetic material. (2 marks)

     

  • Repeatedly suspend each of the bars through its centre of gravity and set it swinging in a horizontal plane about a vertical axis through its centre.
  • The magnetized bar will always come to rest in a north-south direction.(c) Figure 12 shows two identical copper coils X and Y placed close to each other.

    Coil X is connected to a DC power supply while coil Y is connected to a galvanometer.

     

  • (i) Explain what is observed on the galvanometer when the switch is closed. (4 marks) 
  • The galvanometer pointer first defects then moves back when the switch is closed a current builds up in coil X and due to change in flux linkage an emf is induced in coil Y making an induced current flow through the galvanometer during the time current in coil X is rising.When current through coil X is steady no induced current flows through the galvanometer since there is no change in flux linkage. Therefore pointer deflects back.

    (ii) State what is observed on the galvanometer when the switch is opened. (1 mark)

     

  • Pointer deflects in the opposite direction(iii) State what Would be observed if the number of turns in coil Y is doubled. (1 mark)

     

  • Magnitude of deflection increases.l9. (a) Define half life as used in radioactivity. (1 mark)

     

  • Half life is the time taken for half the number if nuclides initially present in a sample to decay.(b) Figure 13 Shows a device used to detect radioactivity by forming tracks when air is ionised.

  • (i) State the name of the device shown. (1 mark) 
  • Expansion cloud chamber/cloud chamber(ii) State how air in the device gets ionised. (1 mark)

     

  • Due to collisions between the radiations from the radiation source and the air molecules. 
  • When the piston is pulled down air expands hence cools The ions form nuclei for condensation upon cooling on which the saturated alcohol vapour condenses+ forming visible tracks(c) (i) State two Factors that determine the speed of the photoelectrons emitted from a metal surface. (2 marks)

     

  • The work function of the metal.
  • Energy of incident radiation/frequency/wavelengthThe energy of a photon of light is 2.21 eV .(electronic charge is 1.6 x 10-19C and planks constant h is 6.63 x 10-34Js).

    I. Express this energy in joules. (l mark)

    1 Energy = eve = 1.6 x 10-19 x 2.21

    =3.54 x 10-19J

    II. Determine the frequency of the light that produces the photon. (2 marks)

    E = hf

    f = e/h

    = 3.54 x 10-19/6.63 x 10-34

    = 5.33 x 10-14Hz

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