TRANSFORMER REVISION QUESTIONS
1. A transformer has a primary coil of 100
turns and a secondary coil of 300 turns. What will be the voltage out of the
secondary coil if we apply 20 V to the primary?
2. If we need to change 240 V down to 12 V,
and our transformer to have 2000 turns on its primary coil, how many turns
should it have on its secondary coil?
3. A transformer has a primary of 6000 turns
and a secondary of 150 turns. The primary is connected to an a.c supply of 240 V.
A 3Ω resistor in
connected across the secondary. Draw a circuit diagram to show the above
arrangement.
Assuming that the
transformer has an efficiency of 100%, calculate;
a)
The
voltage across the resistor
b)
The
current through the resistor
c)
The
current in the primary circuit
d)
The
power taken from the supply
e)
The
power dissipated (wasted as heat) in the resistor
4. A 6 V, 12 W bulb operates from the
transformer connected to a 240 V a.c supply. If there are 8000 turns on the
primary,
a)
How
many turns are there on the secondary?
b)
What
it is the current in the primary?
(Assume that the
transformer is 100% efficient)
5. (a) Briefly explain why most practical
transformers have efficiency less than 100%?
(b) A transformer 600
turns in the primary circuit and 9000 turns in the secondary circuit
is connected to 240 V mains supply. What
is the current in the primary circuit?
(Assume it has 100% efficiency)
6. A transformer with 400 turns in the
secondary circuit and 20 turns in the primary circuit has p.d of 240 V in the
primary circuit. What is the p.d in the secondary circuit?
7. A step-down transformer has 600 turns in
the primary circuit and N turns in the secondary circuit. If it is connected to
240 V mains supply and the voltage in the secondary circuit is 12 V, determine
the value of N.
8. A heater rated 4 W, 12 V is connected to a
secondary circuit of a transformer with 600 turns in the primary circuit. If
the primary circuit of the transformer is connected to 240 V mains, determine
the number of turns in the secondary circuit and the current in the primary
circuit.
9. A radio has a transformer with an output
of 6 V, and a power rating of 9 W. if the primary circuit has 1200 turns and
connected to 240 V mains, determine;
a)
The
current in the secondary circuit.
b)
The
number of turns in the secondary circuit.
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