Form 3 Physics paper 2 Exams and Marking Schemes Free

Name__________________________________________ Adm No __________

Date___________________________________________ Sign______________

JOINT EVALUATION

232/2

PHYSICS

2 HOURS

END TERM III EXAM

FORM THREE

 

INSTRUCTIONS

1. Write your name and admission number in the space provided
2. This paper consists of two sections A and B.
3. Answer all the questions in the spaces provided.
4. All working must be clearly shown.
5. Mathematical tables and electronic calculators may be used.

For Examiner’s Use Only

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

 

 

 

 

 

 

 

 

 

SECTION A (25 MARKS)

Answer ALL the questions in this section in the spaces provided

1. The figure below shows a ray of light incident on the surface of one plane mirror.

Sketch the path of the ray on the diagram after striking mirror 2 indicating all the angles.       (2 marks)

2. Explain why eight dry cells of 1.5V each arranged in series to give a total e.m.f of 12.0V cannot be used to start a car just like a lead-acid accumulator.                                           (2 marks) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
3. When a candle flame is brought near the cap of a charged electroscope, the electroscope discharges. Explain this observation.                               (2 marks) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
4. The figure below shows an experiment set up used to illustrate dispersion of white light.
5. Identify the colours X and Y.             (1 mark)

X   ________________________________________

Y   ________________________________________

1. What physical property changes for the colours when they enter the prism?             (1 mark) ……………………………………………………………………………………………………………………………………………………………………………………………………………………

 

5. Diffraction is not a common phenomenon in light. Explain why.       (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………
6. Apart from temperature, state any one other factor which affects the resistance of a metallic conductor.                                           (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………
7. a) Define the term capacitor.                                                           (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………
8. b) Two plates of a parallel-plate capacitor are 0.6 mm apart and each has an area of 4 cm².Given that the potential difference between the plates is 100 V, calculate the charge stored in the capacitor.

(Take ( E _o =8.85 * 10^-12*Fm^-1)                                                                                     ( 3mks)

 

 

 

 

 

 

 

 

 

 

 

 

 

8. A current of 0.8A flows through an electric circuit. Determine the quantity of charge that passes a point in the circuit in 6 minutes.                                                                      (2 marks)

 

 

 

 

 

 

 

 

 

9. The figure below shows an incomplete circuit of an electromagnet.

Complete the circuit by drawing the windings on the two arms of the core so that A and B are both north poles when the switch S is closed.  Indicate the direction of the current of the windings drawn. (1 mark)

 

 

 

10. A girl standing 120m away from a tall building claps her hands and hears an echo 0.75s later. Determine the speed of sound in air at this place.                                                (3 marks)

 

 

 

 

 

 

 

 

11. The figure below shows a thick copper conductor placed between two poles of a strong magnet. The wire is free to swing in between the poles.
12. Indicate on the same diagram the direction in which the conductor swings when the switch K is closed. (1 mark) ……………………………………………………………………………………………………………………………………………………………………………………………………………………

 

1. State one change that can be made on the set up so that the direction of swing of the conductor is reversed. (1 mark) ……………………………………………………………………………………………………………………………………………………………………………………………………………………
2. The set up in figure 4 below can be used in a laboratory for lifting and releasing a steel ball.
3. State the material which is suitable for use in the core.      (1mark) ……………………………………………………………………………………………………………………………………………………………………………………………………………………
4. If a slightly larger ball is to be lifted, it is necessary to make an electromagnet stronger. Name two ways of increasing the strength of the magnet.                         (2 marks) …………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

 

SECTION B (55 MARKS)

Answer ALL the questions in this section in the spaces provided.

13. a) Sound is a mechanical longitudinal wave. Explain why sound is classified as;
14. A mechanical wave.       (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
15. A longitudinal wave.       (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

 

 

 

 

1. b) The diagram below shows a set up that was used to demonstrate that, sound is a mechanical wave.
2. State the function of the vacuum pump.       (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………
3. When the switch is closed, state and explain what happens as the air is continuously drawn from the bell jar.                                           (3 marks) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

• State two possible reasons why it is not possible to reduce the sound completely in this experiment.                   (2 marks) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

1. c) A fishing boat uses ultrasound to detect fish directly below. Two echoes of the ultrasound are received, one after 0.09 seconds coming from the shoal of fish and the other after 0.12 seconds coming from the sea bed. The sea bed is 84m below the ultrasound transceiver.
2. State two reasons why ultrasound is preferred.       (2 marks) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
3. Calculate the speed of the ultrasound waves in water.       (3 marks)

 

 

 

 

 

 

1. d) State one factor affecting velocity of sound in a solid. (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
2. a) The figure below shows a method of magnetization used in making magnets.
3. Name the method.                   (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………
4. Identify the polarities A and B of the magnet produced.                   (2 marks)

A   ____________________________

B   ____________________________

• Apart from this method, state any other method used in magnetization.                   (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………

1. b) In demagnetization by electrical method:
2. State the type of current used.       (1 mark) ………………………………………………………………………………………………………………………………………………………………………………………………………………
3. Explain your answer in (i) above.                   (2 marks) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
4. Explain why when demagnetizing a magnet, the magnet should be held in the East-West direction.

(2mrks) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

 

15. a) Define the following terms ( 3 mks)

1. Principal focus ………………………………………………………………………………………………………………………………………………………………………………………………………………
2. Centre of curvature ………………………………………………………………………………………………………………………………………………………………………………………………………………

• Focal plane ………………………………………………………………………………………………………………………………………………………………………………………………………………

1. b) An object is placed 18 cm in front of a concave mirror of focal length 12 cm. Determine the position and nature of the image formed                                         (3mks)

 

 

 

 

 

 

 

 

 

 

1. c) The graph below shows variation of (cm ^-1) against   (cm ^-1) with for an object placed in front of a concave mirror

 

From the graph,

1. Determine the focal of the mirror.       (2mks)

 

 

1. Determine the image distance when the object is 20cm from the mirror.       (2mks)

 

 

16. a) The figure below shows how a student set up a circuit using 3 identical bulbs X, Y and Z each rated “12V, 2.0A”
17. When operating normally, calculate the resistance of one of the bulbs       (2 Marks)

 

 

 

 

 

 

 

1. Calculate the effective resistance of the three bulbs.       (2 Marks)

 

 

 

 

 

 

• What will be reading of the ammeter?       (2 Marks)

 

 

 

 

 

 

1. Draw a circuit diagram showing the three bulbs connected in such a way that they would all work at the same brightness especially if they are not identical.                                          (2 Marks)

 

 

 

 

 

1. b) When the switch S is kept open in the circuit shown below the voltmeter reads 1.5V. When the switch is closed, the readings drops to 1.3V and the current through the resistor is 0.5A.
2. What is the e.m.f of the cell?       (2 Marks)

 

 

 

 

1. What the terminal voltage of the cell?       (1 Mark)

 

 

 

• Calculate the value of R.       (3 Marks)

 

 

 

 

 

17. a) Sketch a graph of displacement against time for a transverse wave of frequency of 50Hz of at least two cycles with amplitude 2cm.       (4marks)

 

 

 

 

 

1. b) State two factors affecting velocity of sound in air (2marks) …………………………………………………………………………………………………………………………………………………………………………………..…………………………………………..
2. c) State two uses of echoes. (2 marks) ………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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PHYSICS PP2 MARKINGSCHEME FORM 3

Incident light ray

              All the angles must be indicated

2. Eight dry cells in series have a very high internal resistanceü1 hence very little current can be drawn from themü1
3. The flame ionizes air producing both positive and negative ionsü The ions opposite to the charge of the electroscope are attracted to the cap of the electroscope causing dischargeü1.

 

Give 1mk if the two are correct

1

• (a) X – Violetü

Y    –      Red ü

(b) Velocity ü1

5. Light waves have very short wavelength.ü1
6. – Length of the conductor.ü1

• Cross section area of the conductorsü1

7. a )Is a device used for storing charge

b ) C=E_OA/d

    = 8.85*10^-12*4*10^-4/6*10^-4

  = 5.9*10^-12

  =5.90pF

      Q = CV

  =590*10^-9*100

   =  5.9*10^-10C

8. Q = It

= 0.8 x 6 x 60C P¹

\Q = 288C     P¹                    (Units must be shown)

9. .

 

 

 

 

 

 

10. P¹

P¹

\Speed = 320m/sP¹

 

11. (a)

 

 

 

 

• – Reversing the direction of flow of electric current in the conductor.

– Reversing the direction of magnetic field;

 

12. .i) Soft ironü1 since it is easily magnetized and
13. ii) –           Increasing the amount of current ü1

• Increasing the number of turns on the coilü1

13,.      a)     i)         it requires a medium for transmission. ü1

1. ii) It is propagated as a series of alternating compressions (High pressure zones) and rarefactions (Low pressure zones)ü1OR

The direction of the wave travel is parallel to the disturbance that produces it ü1 (Any one)

1. b) i)     To evacuate the bell jar ü1 OR

To pump air in and out of the bell jar                      ü1 (Any one)

1. ii) The electric bell starts ringing but its sound as heard from outside the bell jar reduces in intensity and diminishes. ü1 This is because as the air is pumped out, the density of air in the bell jar reduces. ü1 As this continues a vacuum is created in the bell jar which cannot transmit soundü1hence the sound get diminished

iii) –      It is not possible to create vacuum in               the bell jar ü1

–      Some sound is transmitted through      the connecting wires and the walls of        the bell jar.ü1

1. c) i)     –      It penetrates deepest. ü1

–      It can be reflected easily by tiny grains.ü1

1. ii) S = Þ D = 84 x 2 = 164m

T = 0.12s

S =  = 1400 m/s ü1

1. d) -Temperature of the solid√

    -Density of the solid√

14     a)       i) Double stroke method. ü1

1. ii) A    – South poleü1

B    – North poleü1

iii) –      Induction method.ü1

• Mechanical method – Hammeringü1
• Electrical method.ü1 (Any one)

1. b) i)    Alternating current (a.c)
2. ii) It reverses many times per second,  ü1 disorienting the magnetic                               ü1
3. c) So that they don’t retain any magnetismü1 due to earth’s magnetic field.ü1

 

15. a( i) For a concave mirror ,is the point at which all rays parallel and close to the principal axis converge after reflection. For convex is the point at which all rays parallel and close to the principal axis appear to diverge from after reflection by the mirror

 

( ii) Is the centre of the sphere of which the mirror is part

(iii) Is a plane perpendicular to the principal axis  and  passes through the principal focus

 

1. b) u=+18 cm

f= +12 cm

using 1/v+1/u=1/fü

1/v+1/+18=1/+12ü

1/v+1/18=1/12

1/v=1/12-1/18

1/v=-1/36

V=-36 cmü

 

1. c)

	I u
			I v

 

 

 

 

 

 

(i)       I – intercept = 0.07

u

I = 0.07

f

f = 0.07  = 1/ 0.07

= 14.29cm

 

(ii)    I =  I  +   u

f     u       v

 

I            = I  +  I

14.29       20    v

 

I   =  1        –   1

V   14.29        20

= 0.07 – 0.05

= 0.02

 

V  =     1

0.02

= 50cm

 

16. (a) (i) = V = IR Þ R =

= ü

= 6Ωü

(ii) Y, Z are parallel

=  +

= 3Ω ü

X in series with

Þ = (6 + 3)

= 9Ω ü

(iii) I = ü

=

= 1.333A ü

(iv)

ü

ü

 

(b)  (i)  E.m.f = 1.5V

(ii) Terminal voltage = 1.3V

(iii) R =

=

= 2.6Ω

Axes correctly labelled;ü 2 complete circles:ü T= 1/50 = 0.025; ücorrect time indicated;ü

 

 

 

 

1. b) Direction of the wind ; ü

Temperature of the airü

Humidity of the air

 

1. c) -Determining the speed of sound in air√ 1

-Determining distances using pulse echo-technique√ 1