SECTION A (25 MKS)
Answer all the questions in this section in the spaces provided below each question
- Figure 1 shows a ray of light XY striking the mirror CD held at an angle of 108º to mirror DE.
Complete the path of the ray XY and state the final angle of reflection. (2 mks)
- Figure 6 below shows a progressive wave incident from a shallow end to a deep end.
- Sketch the appearance of the wave in the deep region. (1mk)
- State the property of waves demonstrated in the figure above. (1mk)
- State a device where a variable air capacitor could be used. (1 mk)
- Figure 2 below shows a metre rule in equilibrium balanced by the magnet and weight. The iron core fixed to the bench.
State and explain the effect on the metre rule when the switch S is closed. (2 mks)
- An electric kettle is rated at 1.8 kW, 240 V. Explain the choice of the safest fuse for the kettle. (the available fuses are 5 A, 10 A, and 20 A). (3mks)
- The chart below shows an arrangement of electromagnetic spectrum.
radio waves A infra-red visible light B x-rays gamma rays
- Name the radiation represented by A (1mk)
- Name the device that can be used to detect radiation B (1mk)
- An uncharged metal rod brought close but not touching the cap of a charged electroscope causes a decrease in the divergence of the leaf. Explain. (1 mk)
- Figure 10 below shows capacitors connected to 3v supply.
Calculate the total charge in the circuit. (3mks)
- Explain how polarization affects the working of a simple cell. (2mks)
- A siren has 200 holes and makes 30 revolutions per minute. If the speed of sound waves produced is 340m/s, determine the wavelength of sound produced. (2 marks)
- Write one difference between a virtual and a real image. (1mk)
- The figure1. Shows an object, O placed in front of a concave lens. By drawing appropriate rays, locate the image formed. (3mk)
- Mention one factor that determines the current carrying capacity of lead acid accumulator (1mk)
SECTION B (55 MKS)
- The figure below shows an X-ray tube.
- Label the part marked Y. (1 mk)
- How would one increase
- The intensity of the X –rays. (1 mk)
- Penetrating power of the X –rays. (1 mk)
- Explain why the tube is highly evacuated. (2 mk)
- An X –ray tube operating with an anode potential of 10 kV and current of 15mA.
- Calculate the number of electrons hitting the anode per second. (3 mk)
- Determine the speed with which the electrons hit the target (3 mk)
(charge of an electron, q=1.6 x 10-19C, mass of an electron Me=9.1 x 10-31 kg.)
- State what is meant by electromotive force (e.m.f) of battery. (1mk)
- Three identical bulbs are connected in series with a battery of dry cells. At first the bulbs shine brightly but gradually become dimmer. Using the same cells, explain how you would increase the brilliance of the bulbs. (2mks)
- The graph in figure 8 shows the terminal voltage, V, of a certain battery varies with the current, I, being drawn from the battery.
- Write an expression relating the e.m.f. E, terminal voltage, V, current, I and the internal resistance, r, of the battery for the circuit drawn in (i) above. (1mk)
- From the graph determine the;
- Internal resistance, r, of the battery. (3mks)
- e.m.f., E of the battery (2mks)
- On the axes provided, sketch a graph to show how current, I varies with potential difference, V, across a metallic conductor that is being heated at the same time. Explain your answer (2mks)
- What is meant by
- Radioactive decay? (1mk)
- Background radiation. (1mk)
- State one possible source of background radiation. (1mk)
- Radiation from a radioactive source enters a G.M tube.
- State the effect of the radiation on the gas inside the tube. (1mk)
- Explain how the large discharge current is created. (2mk)
- The diagram in the figure below shows paths taken by three radiations K, J and L from a radioactive through an electric field.
- State the charge on plate A (1mk)
- Identify the radiations K and L. (2mks)
- Give a reason why L deviates more than K (1mk)
- For a certain radioactive material, the average count-rate is found to be 82 counts per second. After 210 seconds, the count rate had dropped by 63 counts per second. The average background count-rate remained constant at 10 counts per second. What is the half-life of the material? (3mks)
- What is meant by
- An optical fibre provides an efficient way of transmitting light energy. State and explain the property of light behind its functioning. (2mks)
- State one condition under which the above property occurs. (1mk)
- Figure 6 shows a slab of glass of uniform thickness lying horizontally. Above it is a layer of water. A ray of light PQ is incident upwards on the lower surface of the glass and is refracted successively at A,B and C, the points where it crosses the interfaces.
(Refractive index of glass = 3/2 , refractive index of water = 4/3)
- Angle x (3mks)
- The refractive index for light passing from the glass to water. (2mks)
- Angle y (2mks)
- State the main difference between an induction coil and a transformer. (1mk)
- The figure below is a simple microphone in which sound waves from a speaker cause the cardboard diaphragm to vibrate.
- Explain how a varying current is induced in the coil when the diaphragm vibrates to and fro. (3mks)
- State two ways in which the induced current in 18b(i) above can be increased. (2mks)
- Define flux leakage as used in transformers. (1mk)
- How is it minimized? (1mk)
- In the design of a transformer in a (i) above which coil would be made with thick conductors if the transformer is a step-up. (1mk)
- Explain your answer in b (i). (1mk)
√- Correct direction of reflected ray
√- Final angle of reflection = 60o
property--- variation of wavelengths when wave fronts move from shallow to deep region
- in a radio tuning circuit
- The metre rule will tip in anticlockwise direction√. This is because when the switch S is closed the iron core becomes magnetized with the top of the core becoming a south pole√ hence attracts the north pole of the magnet.
- I =1800/240 = 7.5 A√ safest fuse = 10 A√ which is slightly above the operating current√.
- Micro wave
- Photographic film, photocell, fluorescent materials
- Metals get charged by induction, the charges are transferred from the electroscope this causes earthing, / charges on the electroscope induce opposite charges on the conductor.
- Total capacitance = 2(8) + (2.4) = 4.0µf√
Q = CV
= 4(3) √
= 12µC √
- Hydrogen gas insulates copper plate√ thus increasing the internal resistance√ of the cell
- f = no. of holes × rev. per sec.
= 200 × 30/60 = 100Hz √
λ = V/f = 340/100
- Real images are formed on the screen while virtual images appear behind the screen.
√ a mark for each ray
√ for correct position of image
- Area of each plate
Number of plates
- Cooling fins /copper fins .
- Increase the cathode heater current .
- Increasing the anode potential
- To prevent energy loss by electrons this results from collisions with the air particles
- Q=It=15 x 10-3 x1= 15 x 10-3C
N= Q/e =15 x 10-3 = 9.4 x 1016 electrons
1.6 x 10-19
- V= √ 2eV =√2 x 1.6 x 10-19 x10,000
me 9.1 x 10-31
=5.93 x 107m/s
- Q=It=15 x 10-3 x1= 15 x 10-3C
- E.m.f is the p.d. across the battery in the ü1 open circuit while terminal voltage is the p.d. across the cell is a closed circuit.
- By Connecting the bulbs in parallel, √ this lowers the total resistance in the circuit thus the brightness increases.
- E = V+Ir
- E = IR + Ir
V = E - Ir
V = -Ir + E
Slope -r = 1.5 - 1.0 = 0.5 = -0.78
0.16 - 0.8 -0.64
r = 0.78Ω
- E.m.f = 1.625V
The resistance of the metallic conductor increases with increase in its temperature.
- Radioactive decay is the spontaneous random disintegration of an unstable nuclide to form a stable nuclide.
- Counts registered in the absence of a radioactive source;
Radiations present on the surface of the earth and in the atmosphere 1mk
- Cosmic radiation from the sun
- Radio isotopes in the earth’s rocks
- Nuclear waste from nuclear power stations
- Screen of TV
- Some paints are radioactive.
- ionizes the gas
- Ions are attracted towards electrodes
Collision with other molecules cause avalanche of ions which on attraction to electrodes cause discharge.
- K—Alpha Radiation L- Beta Radiation
- K is more massive than L
- No = 82 - 10 = 72
N = 19 - 10 = 9
72 → 36 → 18 → 9
3 - half line = 210
1 half life = 210/3 = 70 seconds.
- Total internal reflection.
Rays of light undergo total internal reflection repeatedly on the boundary of high and low refractive index the entire length of the fibre.
- Light must be traveling from optically denser to a less dense medium
The angle of incidence in the denser medium must be greater than the critical angle
- sin 60º = 1.5
sin x = sin 60º= 0.5774
x = Sin-1 (0.5774)
- gnw = gna ×. anw
= 2/3 x 4/3
- sin 35.26º = 8/9
y = sin-1(0.6494)
Y = 40.5º
- sin 60º = 1.5
- Total internal reflection.
- An induction coil uses direct current while a transformer uses alternating current.
- As the diaphragm vibrate to and fro due to sound wave impact, it causes the coil to move forth and back cutting through the magnetic field lines. This causes a varying electromotive force to be induced in the coil which causes a varying current to flow.
- Increase impulsive force of sound waves to diaphragm
Increase sound frequency
Increase no. of turns
Increase strength of magnet / use magnet with closer poles
- Occurs when some of the magnetic flux produced by the primary coil does not link up with the secondary coil.
- Secondary coil wound on top of the primary coil
- Primary coil
- It carries more current than the secondary coil in a step up transformer and should have very little resistance.