K.C.S.E Physics Q & A - MODEL 2016PP2QN18
​(a)State one factor that affects the speed of sound in a solid.
b)An observer stands half-way between two vertical cliffs that are L metres apart.He strikes a gong and measures the time interval, t, between the echoes heard from the two cliffs. He moves a further 10m and again strikes the gong and measures the time interval between the echoes. The process is repeated several times. The graph in Figure 13 shows the relation between the time interval, t and the distance, x from the centre. (i)From the graph, determine the value of x for which the time interval was 0.55. 
​(ii)Given that t = 4x/v where v is the speed of sound in air, determine the value of v from the graph.
(iii)If the maximum time measured by the observer was t=4.7s, determine the distance L between the cliffs. (c)A search boat uses a signal of frequency 6.0 x 104 Hz to detect a sunken ship directly below. Two reflected signals are received; one after 0.1 seconds from sunken boat and the other after 0.14 seconds from the sea bed. If the sea bed is 98 m below the boat, determine:- (i)The speed of the signal in water. You may use the value of v from (ii) above. (ii)The depth of the sunken ship below the boat
answers
​(a)Temperature
Density (b)(i)47 metres (ii) 
​(iii)Distance = speed x time
2D = distance to and from the cliff 2D = 340.715 x 4.7 D = 800.68 metres (c)(i)Distance moved by sound from sea bed = 98 x 2 m V = (98 x 2)0.14 = 1400 m/s (ii) Distance = v x t = 1400 x 0.10/2 = 70 m
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K.C.S.E Physics Q & A - MODEL 2016PP2QN17
​When a radiation was released into a diffusion cloud chamber, short thick tracks were observed. State with a reason, the type of radiation that was detected.
(b)The half-life of an element X is 3.83 days. A sample of this element is found to have an activity rate of 1.6 x 10^3 disintegrations per second at a particular time. Determine its activity rate after 19.15 days. (c) State what is meant by an extrinsic semiconductor. (d)Figure 11, shows a depletion layer in an unbiased p-n junction 
​State how a battery can be used to make the depletion layer narrower.
(e)Figure 12, shows an incomplete circuit of a full wave rectifier. 
​(i) Draw in the figure two more diodes to complete the circuit should be obtained.
answers
​(a)Alpha radiation. This radiation has a short range with intense ionization hence thick tracks
​(c)It is a semiconductor in which impurities have been added to change conductivity
​(d) By connecting it in a forward biased mode
​(ii)Across QS
K.C.S.E Physics Q & A - MODEL 2016PP2QN16
​Figure 8, shows a circuit that may be used to charge a capacitor.
(i) state the observation on the milliameter when the circuit is switched on:
(ii) explain the observation in (i) above. b)The circuit in figure 8 is left on for some time. State the value of p.d. across: (i) the resistor R; (ii) the capacitor C; (c) sketch the graph of potential difference (V) across R against time. ​(d) Figure 9 shows three capacitors connected to a 10V battery 
​Calculate:
(i) the combined capacitance of the three capacitors; (ii) the charge on the 5.0 uF capacitor.
answers
​(a)(i)Current falls off to zero.Falling to zero deflects to maximum then zero.
(ii)Current flows when the capacitor is charging. When fully charged no current flows and potential difference (p.d.) is equal to charging voltage (b) (i)VR = 0 volts (ii)Vc = 5 Volts 
K.C.S.E Physics Q & A - MODEL 2016PP2QN15
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 ac. Mains supply. i) 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 it is 0.80A.
answers
(a) ​(i)The galvanometer will be deflected to one side and then back to zero.
(ii)A greater deflection will be obtained in the opposite direction as the current takes less time to die off than to build up b)(i)The changing current in the primary coil induces a current in the secondary coil due to changing magnetic field of the primary current ii)Ns/Np = Vs/Vp hence Vs = (240 x 200)/1000 = 48V iii)Efficiency = power output/Power input x 100 (4.8 x 0.8 x 100)/240 x 0.2= 80% K.C.S.E Physics Q & A - MODEL 2016PP2QN14
​Figure 6 shows a simple electric bell circuit
​(i)Name the parts labeled
(I) D (II) E (ii)When the switch is closed, the hammer hits the gong repeatedly. Explain why: (I) the hammer hits the gong. (II) the hammer hits the gong repeatedly. (b) An electric bulb is rated 60 W, 240 V. Determine: (i) the current that flows through it when it is connected to a 240 V supply. (ii) the resistance of the bulb.
answers
​(i)D-Soft iron armature
E-Contact screw (ii) (I)Soft iron core is magnetized It attracts the armature (II) Contact is broken The core then loses magnetism Armature spring back making contact again 
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