K.C.S.E Physics Q & A - MODEL 2018PP2QN18
​(a) (i) Draw a circuit diagram showing the depletion layer of a p—n junction diode connected in the reverse bias mode.
(ii) State the reason why increasing the external voltage in (i) makes the depletion layer wider. (iii) State the meaning of breakdown voltage of a junction diode. (iv) State one application of diodes. (b) Figure 7 shows the output on a screen of a CR0 when an a.c. signal is connected to the Y-plates with the time base on. 
​(i) Given that the time control is 5 ms per division and the y-gain is 100 V per division determine the:
(I) frequency of the ac. signal (II) peak voltage of the input signal (ii) State the adjustment that may be made in order to halve the frequency of the a.c. signal.
answers
​(ii) The holes and the electrons in their respective regions are attracted away from the junction by the external voltage.
(iii) The voltage at which the diode begins to conduct in the reverse bias mode. (iv) In rectification circuits for changing a.c. to d. c. In control of voltages of Zener diode. 
​(iii) Double the time control to 10ms per division.
Adjust the frequency of the source to half the value
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K.C.S.E Physics Q & A - MODEL 2018PP2QN09
​A transformer has 600 turns in the primary coil and 9000 turns in the secondary coil. The transformer is 100% efficient and the current in the secondary coil is 0.15A, determine current in the primary coil.
answer
K.C.S.E Physics Q & A - MODEL 2017PP2QN17
​(a) Figure 8 shows a conductor AB connected to a galvanometer and placed between two permanent magnets.
​(i) Conductor AB is moved perpendicular to the magnetic field.
State and explain the observation made on the galvanometer. (ii) State the effect of moving the conductor faster. (b) A transformer is used to step down 240V to 12 V for use in an electric appliance operating at 0.5 A. If the primary coil has 600 turns, determine the; (i) number of turns ¡n the secondary coil, (ii) current in the primary coil.
answers
​ a) i. A momentary deflection is observed, Conductor cuts the field.
An emf is induced in AB Causing current in the circuit ii. A bigger deflection is observed! higher current 
K.C.S.E Physics Q & A - MODEL 2017PP2QN08
Draw a circuit diagram to show a p-n junction diode in the forward biased mode.
answer
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
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