K.C.S.E Physics Q & A - MODEL 2012PP2QN016
(a) Figure 15, shows two coils A and B placed close to each other. A is connected to a steady D.C supply and a switch, B is connected to a sensitive galvanometer.
(i) The switch is now closed. State the observation made on the galvanometer.
(ii) Explain what would be observed if the switch is then opened. (b) The primary coil of a transformer has 1000 turns and the secondary coil has 200 turns. The primary coil is connected to a 240V a.c mains, supply. (1) Explain how an e.m.f is induced in the secondary coil. (ii) Determine the secondary voltage. (iii) Determine the efficiency of the transformer given that the current in the primary coil is 0.20A and in the secondary coil is 0.80A.
answers
(a) (i) Pointer deflects upto a certain; maximum value and then returns to zero;
(ii) There is a deflection in the opposite direction then back to zero; As Flux in A falls, flux in B also falls and causes induced e.m.f in the opposite directions; (b) (i) Current in the primary is constantly changing its direction; so that the resulting flux (which link coils) is constantly changing its “ direction. Therefore alternating e.m.f is induced in the secondary coil;
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K.C.S.E Physics Q & A - MODEL 2012PP2QN015
Figure 14, shows a circuit in which a battery, a switch, a bulb, a resistor P, a variable resistor Q, a voltmeter V and two ammeters A1 and A2 of negligible resistance are connected.
P has a resistance of 10Ç2. When the switch is closed A1 reads 0.1OA and the voltmeter reads 1.5V.
(a) Determine; (i) the current passing through P. (ii) the resistance of the bulb. (b) The variable resistor is now adjusted so that a larger current flows through A2. (i) State how this will affect the resistance of the bulb. (ii) Explain your answer in b(i). (c) A house has one 100W bulb, two 60W bulbs and one 30W bulb. Determine the cost of having all the bulbs switched on for 70 hours, given that the cost of electricity is 40 cents per kilo-watt hour. K.C.S.E Physics Q & A - MODEL 2012PP2QN014
(a) Figure 12, shows a displacement - time graph for a progressive wave.
(i) state the amplitude of the wave.
(ii) determine the frequency of the wave. (iii) given that the velocity of the wave is 20m/s,determine its wavelength. (b) Figure 13 shows two identical dippers A and B vibrating in water in phase with each other. The dippers have the same constant frequency and amplitude, The wavesproduced are observed along line MN:
It is observed that the amplitudes are maximum at points Q and S, and minimum at points P and R.
(i) explain why the amplitude is maximum at Q. (ii) state why the amplitude is minimum at R. (iii) State what would happen if the two dippers had different frequencies. State why alternating current (a.c) is used for transmitting electricity over long distances21/7/2020
K.C.S.E Physics Q & A - MODEL 2012PP2QN012
State why alternating current (a.c) is used for transmitting electricity over long distances
answer
K.C.S.E Physics Q & A - MODEL 2012PP2QN07
Figure 7, shows two similar coils P and Q around the end L and M of a piece of soft iron. A steady current passes through the coils
State the polarity of the resulting magnet at end L.
ANSWER
K.C.S.E Physics Q & A - MODEL 2012PP2QN05
Figure 5, shows an object O at the bottom of a beaker full of a liquid. An observer above the beaker sees its image at point X inside the liquid.
Determine the refractive index of the liquid.
K.C.S.E Physics Q & A - MODEL 2012PP2QN02K.C.S.E Physics Q & A - MODEL 2012PP1QN18
(a) Figure 12 shows a set up used to determine the mass of a solid S. The rod is pivoted at its centre of gravity C.
(i) State two measurements that need to be made to determine the mass of solid S.
(ii) Write an expression to show how the measurements in (i) above are used to obtain the mass of S. (b) Figure 13 shows a log of wood of mass 20 kg submerged in water in a pond and held in position by a string fixed to the bottom of the pond. Given that the density of water is 1000 kgm3 and that of wood is 800 kgm3, determine the; (i) Volume of the log. (ii) Upthrust on the log. (iii) Tension in the string.K.C.S.E Physics Q & A - MODEL 2012PP1QN17
(a) Figure 11 shows how an underground room was ventilated. It had two vents, one at A and the other at B. A fire was lit at point C.
Explain what happened to the ventilation when the fire was lit.
(b) Explain how a vacuum flask minimizes loss of heat through radiation. (c) In an experiment to investigate the unusual expansion of water, a fixed mass of water at O°C was heated until its temperature reached 20°C. On the axis provided, sketch a graph of density against temperature of the water from O °C to 20°C. (d) An immersion heater rated 2.5 kW is immersed into a plastic jug containing 2 kg of water and switched on for 4 minutes. Determine;
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