ELECTRICITY QUESTIONS
FORMULAE :
Current = Charge x Time
Resistance
= Voltage/Current
Power
= Voltage x Current
Cost
of electrical energy = Power (kW) x Time (hours) x 8p
1. Draw a circuit to
show two door pushes operating just ONE door bell.
2. What is the cost
of the following:
(a)
a 4 kW heater running for 3 hours ..................………………………………....
(b)
a 200 W stereo on for 5 hours . ...................………………………………...
(c)
a 2 kW fan blower on for 30 mins ..........………………………………............
3. Write down THREE safety
precautions that you should take when electricity is used in your
home.
(a)
....................................………………………………...…...............
(b)
..............................................………………………………....…...
(c)
.....………………………………….................................................
4. Draw two circuits, each
containing two lamps and two cells.
The
first one (A) should have the two lamps in parallel and the two cells
in series and the second one (B) should have the two cells in
parallel and the lamps in series.
A.
B.
Which
one will give the brightest lamps? .....…………………………………......
Which one will run
the cells down quickest? .......……………………………………
5. A girl measured
the current flowing through a lamp filament when the voltage was 12.5
V and the lamp was hardly glowing. The reading she got was 10 A.
The
resistance of the lamp was ....…………...…… ohms
She
then turned up the voltage and got the following pairs of readings of
current and voltage.
|
Voltage
(volts)
|
Current
(amps)
|
Resistance
(ohms)
|
|
25
|
8.3
|
|
|
50
|
7
|
|
|
75
|
5.8
|
|
|
100
|
5
|
|
|
125
|
4
|
|
|
150
|
3
|
|
|
175
|
2.7
|
|
|
200
|
2
|
|
Work out the resistance for each
voltage and plot a graph of resistance against current. Plot the
resistance on the y axis and the voltage on the x axis. Use ONE LARGE
square for 10 ohms and ONE LARGE square for 25 volts.
Draw the best-fit
curve on your graph.
The resistance of
the lamp filament increases because:
.....................................................……………………………………………………………….........
