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Programme 19: Circuits
Activity Sheet 3
Ohm’s Law
Using the equation V = IR to solve these
problems.
The resistance of a piece of wire depends on its length. (If you
double the length of the wire you double the resistance.)
- Sam wants to know how much insulated wire there is on a
spool.
- She does an experiment to find the resistance of a 1m length of
wire.
1. a) If voltage V = 4V and current I = 0.8A, what
is the resistance of the 1m piece of wire?
- Next she connects the ends of the wire on the spool to the
voltmeter and the ammeter as in the diagram.
- She measures the voltage and the current for the whole length
of the wire on the spool.
b) If voltage V = 10V and current I = 0.02A, what
is the resistance of the whole length of the wire?
c) Now you have the resistance of 1m of wire, and the resistance
of the whole length, use these numbers to work out how many metres
of wire there are on the spool.
d) The wire was insulated with a plastic sleeve. Explain why the
experiment wouldn’t have worked with wire that wasn’t
insulated.
3.
a) Look at the series circuit. Write down a relationship between
the readings on the voltmeters.
b) Use V = IR to work out the voltage across each
resistor.
c) What is the supply voltage?
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