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.
(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 2014PP2QN14
(a) Figure 6 shows a simple electric bell circuit
(i) Name the parts labelled:
(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 ol the bulb.
(a) (i) I D - soft iron armature
II E contacts
(ii) I. Soft iron core is magnetized and attracts the armature the hammer hits
II. Contact is broken when armature is attracted by the core. The core then loses magnetism.
The armature loses magnetism and springs back making contact again and the process is repeated.
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.
K.C.S.E Physics Q & A - MODEL 2011PP2QN17
(a) State what is meant by the term “electromagnetic induction”.
(b) Figure 9, shows a simple electric generator
(i) Name the parts labelled P and Q.
(ii) Sketch on the axes provided, a graph to show how the magnitude of the potential difference across R, changes with the time t.
(iii) State two ways in which the potential difference produced by such a generator can be increased.
(c) In a transformer, the ratio of primary turns to the secondary turns is 1:10. A current of 500mA flows through a 200 ohms resistor in the secondary circuit.
Assuming that the transformer is 100% efficient, determine:
(i) the secondary voltage;
(ii) the primary voltage;
(iii) the primary current.
K.C.S.E Physics Q & A - MODEL 2011PP2QN07&8
Figure 5, shows a motor connected to a magnetic switch called a relay operated by an ordinary switch S1 Use the information in the figure to answer questions 7 and 8.
Explain how the relay switches on the motor when S1 is closed.
State with a reason the effect on the motor, the iron core is replaced with a steel core and switch S1 is put on and then off.
FORM I - PHYSICS SYLLABUS
FORM II - PHYSICS SYLLABUS
FORM III - PHYSICS SYLLABUS
FORM IV - PHYSICS SYLLABUS
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