1

535/2

Physics 2

SEPTEMBER, 2012

COMPREHENSIVE PHYSICS SEMINAR SEPTEMBER, 2012

St. Denis Sebugwawo S.S Ggaba

Uganda Certificate of Education

INSTRUCTIONS TO CANDIDATES:

Mathematical tables, slide rules and silent non-programmable calculators may be used.

These values of physical quantities may be useful to you.

Acceleration due to gravity = 10 m s-2

Specific heat capacity of water = 4200 J kg-1 K-1

Specific heat capacity of copper = 400 J kg-1 K-1

Specific latent heat of fusion of water = 340000 J kg-1

Speed of sound in air = 320 m s-1

Density of water = 1000kgm-1

© 2012 Internal Seminar

Mechanics and Properties of Matter

1. (a) State the following

(i) Archimedes principle (01 mark)

(ii) The law of floatation (01 mark)

(b) A wooden sphere of mass 6kg and volume 0.02m3 floats on water.

Calculate the

(i) volume of the sphere below the surface of water (04 marks)

(ii) density of the wood (02 marks)

(iii) fraction of the volume of the sphere that would be submerged if it

floats in a liquid of density 800kgm-3 (02 marks)

(c) Explain why a cork stopper held below the surface of water rises when

released (02 marks)

2

2. (a) (i) Define pressure (01 mark)

(ii) State the principle of transmission of pressure in liquids.

(01 mark)

(iii) Give two practical applications of the principle in (a) (i) above

(04 marks)

(b) Describe an experiment to measure atmospheric pressure. (04 marks)

(c) (i) State the principle of conservation of linear momentum (01 mark)

(ii) Two bodies of mass 200kg and 100kg travel towards each other

with velocities of 20𝑚𝑠−1 and 25𝑚𝑠−1 respectively. Find the

common velocity after collision. (03 marks)

(d) A body of mass 5kg is at rest when a horizontal force is applied to it. The

force varies with time as shown in fig. below. Find

50

10 t (s)

F (N)

Fig. 1

(i) The acceleration of the body (02 marks)

(ii) The velocity after 10 seconds. (03 marks)

3. (a) State Newton’s laws of motion. (03 marks)

(b) A block of mass 50 kg is pulled from rest along a horizontal surface by a

rope tied to one face of the block as shown in Fig. 3 below.

Fig 2

The tension in the rope is 220 N. The frictional force between the block

and the horizontal surface is 120 N.

(i) Find the acceleration of the block. (03 marks)

(ii) Calculate the distance moved by the block in 4.0 s. (02 marks)

(iii) What is the reaction of the surface on the block? (02marks)

(iv) Compare the work done by the tension in the rope during the 4.0 s

interval with kinetic energy gained. (06 marks)

3

4. (a) (i) Distinguish between scalar and vector quantities (02 marks)

(ii) Group the following into scalars or vectors; temperature,

momentum; time and displacement. (02 marks)

(b) The graph in Fig. 3 below represents variation of velocity with time of two

athletes A and B.

10 20 30 40 50

2

4

6

8

10

12

14

16

Velo

city

(m

/s)

Time (s)

Fig. 3

A

B

(i) describe the motion of A and B. (04 marks)

(ii) What distance was by covered by B in 50s (03 marks)

(c) A stone of mass 100g is thrown vertically upwards with a force of 5N.

What is its initial acceleration? (𝑔 =10ms-2) (03 marks)

(d) Describe what happens when air is blown into a balloon and the balloon

released. (02 marks)

5. (a) (i) What is meant by the term diffusion (01 mark)

(ii) Explain what is observed when smoke enclosed in an illuminated

transparent cell is viewed through a microscope (02 marks)

(iii) State what is observed in (a) (ii) when the cell is placed on ice

blocks. Give a reason or your answer (02 marks)

(b) (i) Describe an experiment to determine the thickness of an oil

molecule. (05 marks)

(ii) State any assumptions made in (b) (i) above (02 marks)

(iii) In an experiment to estimate the size of a molecule of olive oil, a

drop of the oil, of volume 0.12mm3 was placed on a clean water

4

suface. The oil spread into patch of area 60 ×104mm. Calculate the

size of a molecule of the olive oil. (03 marks)

Heat and Thermal Properties of Matter

6. (a) Distinguish between specific heat capacity and heat capacity

(b) Explain how a hot body standing on a metallic table on the surface of the

moon loses heat

(c) Outline the steps and precautions needed in measuring the specific heat

capacity of a liquid by method of mixtures

7. (a) (i) Distinguish between heat capacity and specific heat capacity

(ii) Explain why the boiling point of a liquid depends on altitude

(b) (i) Give two ways how heat losses are reduced in a thermos flask.

(ii) Describe an experiment to determine the specific heat capacity of a

solid

(c) A copper block of mass 250g is heated to a temperature of 145°C and then

transferred to a copper calorimeter of mass 250g which contains 250cm3

of water at 20°C

(i) Calculate the maximum temperature attained by water

(ii) Sketch the graph to show the variation of temperature with time

(d) (i) What is meant by the term temperature

(ii) Give two physical properties which change with temperature

Propagation and Transmission of Light and Optical

Instruments

8. (a) Explain dispersion as applied to light. (01 mark)

(b) (i) What is a pure spectrum? Give an example of a pure spectrum

(01 mark)

(ii) With he aid of a labelled diagram, describe briefly how a pure

spectrum is produced. (05 marks)

(c) (i) Distinguish between a primary and a secondary colour. Mention

one primary and one secondary colour you know (03 marks)

(ii) Fig. 4 below shows colours mixed by addition. Name the colours

represented by the parts labelled A, B, C and D. (04 marks)

5

D

B

Blue

Green

Red

A

C

Fig 4

(d) Explain briefly what happens when white light falls on green dress.

(02 marks)

9. (a) What is meant by a light ray? (01 mark)

(b) With the aid of a labelled diagram, describe the structure and working of

a simple lens camera (05 marks)

(c) State two differences and two similarities between the human eye and

lens camera (04 marks)

(d) (i) State the laws of refraction of light. (02 marks)

(ii) Fig. 5 below shows a ray of light incident on a right angled prism of

refractive index 1.5.

A ray

of light

Glass P Q

R

Fig. 5

Explain why the ray of light follows the path shown. (04 marks)

10. (a) Define the following terms as applied to curved mirrors

(i) centre of curvature (01 mark)

(ii) principal axis (01 mark)

(b) Explain with the aid of ray diagrams, why a parabolic mirror is preffered

to a concave mirror as a car head lamp (04 marks)

(c) An object of height 15cm is placed in front of a concave mirror of radius of

curvature 20cm. by scale drawing, find the

(i) image distance from the mirror (02 marks)

(ii) height of the image (02 marks)

(iii) linear magnification (01 mark)

6

(c) (i) With the aid of ray diagrams explain how regular and diffuse

reflections are produced (03 marks)

(ii) State the characteristics of images formed in plane mirrors

(02 marks)

Propagation and Transmission of Waves

11. (a) What is meant by the following terms

(i) Standing wave (ii) wave length

(iii) reverberation

(b) A fishing boat uses ultra sound of frequency 6.0 × 104 Hz to detect fish

directly below. Two echoes of the ultra sound are received, one after 0.9 s

coming from a fish and another after 1.2 s coming from the sea-bed. If the

sea bed is 84m below the ultra sound transmitter and receiver, calculate:

(i) the speed of ultrasound in water

(ii) the wave length of ultra sound waves in water

(iii) the depth of the fish below the boat

(c) Distinguish between light and sound waves.

(d) A tuning fork of frequency 512 Hz produces resonance in a tube of length

10.5 cm and also in one of length 91.5 cm. Calculate

(i) The wave length of the sound in the air column

(ii) the velocity of sound in the air column.

12. (a) Define the following as applied to wave motions:

(i) frequency

(ii) wave length

(b) What are transverse waves? (01 mark)

(c) A radio station transmits signals at a frequency of 103.7MHZ. Find the

wave length of the signals and sate any assumption made. (02 marks)

(d) Draw a diagram to show the pattern for straight water wave passing

through a narrow slit. (02 marks)

(e) Describe an experiment to demonstrate that sound waves require a

material medium for their propagation (06 marks)

(f) Explain how sound waves travel through air (03 marks)

Electricity and Magnetism

13. (a) What is meant by a conductor and an insulator? Give an example of

each (03 marks)

(b) (i) Explain briefly how you can charge a conductor negatively by

induction. (05 marks)

(ii) Describe how it can be confirmed that the conductor in (b) (i) is

negatively charged. (02 marks)

(c) Explain the action of a lightning conductor. (06 marks)

7

14. (a) (i) State Ohm’s law and its limitations. (02 marks)

(ii) Sketch the 𝐼 − 𝑉 characteristics of an Ohmic and non-Ohmic

conductors (02 marks)

(iii) Describe with the help of a suitable diagram how you can verify

Ohm’s law. (05 marks)

(b) A galvanometer has a resistance of 5Ω and a range of 0 − 40 𝑚𝐴. Find the

resistance of the resistor which must be placed in parallel with the

galvanometer if a maximum current of 10𝐴 is to be measured. (03 marks)

(c) Four resistors are connected in the circuit as shown in the figure below.

A A

V2

5

3

2

2

C D

Fig. 6

Assuming the internal resistance of the cell and ammeters are negligible,

find:

(i) the total resistance of the circuit

(ii) the current through ammeter D

(iii) current through ammeter C

(iv) power dissipated in the 3Ω resistor.

15. (a) (i) What is meant by electromotive force?

(ii) A dry cell supplies a current of 1.2A through two 2Ω resistors

connected in parallel. When the resistors are connected in series,

the current flowing in the circuit is o.4A. Find the electromotive

force of the cell.

(b) A heater is rated 750W, 240 V.

(i) What does the statement 750W, 240V mean?

(ii) Calculate its resistance

(iii) Find the cost of running three such heaters for four hours a day for

a week given that the cost of electric energy is 45/= per unit.

(c) A coil of resistance wire is immersed in a liquid in a calorimeter of total

heat capacity 950 JK-1. If the temperature rises from 9oC to 39oC in 5

minutes when a steady current of 4 A is passed, find:

(i) the resistance of the coil

(ii) the p.d across it.

8

16. (a) Define the following terms as applied to earth’s magnetism

(i) Magnetic north (ii) magnetic meridian

(iii) Geographical meridian (iv) magnetic field

(iv) Magnetic saturation (vi) Angle of dip

(vii) magnetic variation/declination

(b) Sketch the resultant magnetic field patterns for the following:

(i) Two bar magnets placed with S-poles facing each other

(ii) Two bar magnets placed close to each other and are parallel

(iii) A bar magnet placed in the earth’s magnetic field

(iv) A wire carrying current (inside and out)

(v) Two wires carrying current in opposite directions

(vi) Two wires carrying current in the same direction

(vii) Current through a circular coil

(viii) a solenoid

(ix) a wire carrying current in the earth’s field

(x) Two bar magnets paced with opposite poles close together and are

parallel

(c) Give the ways in which the strength of a magnet can be increased. With

the aid of a labeled diagram, describe the principle of action of a moving

coil loudspeaker/receiver.

17. (a) (i) What is meant by the term electromagnetic induction?

(ii) State the laws of electromagnetic induction

(iii) Outline the ways of increasing the magnitude of induced e.m.f in a

coil. Also define the terms self induction and mutual induction.

(b) (i) Describe the structure and mode of action of an a.c transformer.

(ii) Differentiate between the types of transformers. Describe the

causes of energy losses in a transformer. How can these losses be

minimized.

(c) A transformer of efficiency 80% is connected to a 240V a.c supply to

operate a heater of resistance 200Ω. If the current in the primary circuit

is 5A.

(i) calculate the p.d across the heater.

(ii) if the transformer is cooled by oil of specific heat capacity 2100 Jkg

1k-1 and temperature of oil raises by 25 K in 3 minutes, find the

mass of the oil in the transformer.

Modern Physics

18. (a) (i) What is meant by cathode rays? (01 mark)

(ii) With the aid of a labelled diagram, describe how cathode rays are

produced by thermionic emission (05 marks)

(iii) State three factors which affect the production of cathode rays in a

cathode ray tube by thermionic effect (03 marks)

(b) With reference to the cathode ray oscilloscope, explain:

9

(i) the function of the time base (02 marks)

(ii) how the brightness is regulated (02 marks)

(c) A cathode ray oscilloscope with time base swithed on is connected across a

power supply. The wave form obtained is as shown in fig. below. Distance

between two lines= 1𝑐𝑚

B A

Fig. 7

(i) identify the type of voltage generated by the power supply

(ii) find the amplitude of the voltage generated if the voltage gain is

5Vcm-1.

(iii) calculate the frequency of the power source if the time base setting

on the CRO is 5.0×10-3scm-1.

19. (a) (i) What is meant by radio isotopes?

(ii) State one medical and one industrial use radio isotopes

(b) Describe what happens when a beam of radiation consisting of,𝛼,𝛽 𝑎𝑛𝑑 𝛾

rays is incident on a thin sheet of lead.

(c) The diagram below shows the essential parts of an x-ray tube.

B

A

C

F

D E

Fig. 8

(i) name the parts labeled A, B, C, D E and F

(ii) state the functions of each part

(iii) describe how x-rays are produced

(d) What safety precautions must be taken in an x-ray laboratory?

10

20. (a) What is meant by

(i) half life

(ii) radio activity

(b) What happens to the activity of a radioactive material when its

(i) mass is increased

(ii) temperature is increased

(c) A material is wrapped in photo graphic film and kept in a dark room.

When the photographic film is removed, it is found to be darkened.

(i) identify the material

(ii) explain the observation

(d) A radioactive substance of mass 60g takes 400years for its mass to be

reduced to 15g. Find its half life.

(e) State:

(i) two industrial and two medical uses of radioactivity

(ii) two health hazards of radioactivity

GOOD LUCK