Page 78 - Physics_Form_2

Physics for Secondary Schools
Solution
(a) Energy = power  time
5h
 40 W   30 days
days
FOR ONLINE READING ONLY
= 6 000 Wh = 6 kWh
Therefore, the electrical energy
consumed for 30 days is 6 kWh.
(b) To determine the electricity cost of
watching this TV, we use the formula;
cost  Tsh  price  total units supply. Calculate:
Therefore,
229.60 Tsh
cos (Tsh)t   6kWh
1 kWh
=1 377.60 Tsh
Hence, the cost of watching this TV
for 30 days is Tanzanian shillings
1377.60.
Exercise 2.3
1. A 120 V circuit is equipped with a 20
A fuse. What is the least resistance
that can be plugged into the circuit
without causing the fuse element to
melt?
2. A car’s headlights consume a power
of 40 W when on low beam and
50 W when on high beam. Given
that the headlights are connected
to a 12 V battery, determine:
(a) The current that flows through
the headlight in each case.
72
Physics Form 2 Final.indd 72
(b) The resistance of the headlight
in each case.
3. A generator at a power station has
an output of 100 MW at 132 kV.
(a) What is the current in the
generator?
(b) What is the daily energy output
of the generator in joules and
kilowatt-hours?
4. An electric motor draws a current
of 10 A when connected to a 120 V
(a) The motor’s power consumption.
(b) The energy used by the motor
(in joules and kilowatt-hour)
during 5 hours of operation.
5. A house has five rooms, each with
a 60-W, 240-V bulb. If the bulbs
are switched ON from 7.00 p.m. to
10.30 p.m., determine the power (in
kilowatt-hour) consumed per day.
6. A light bulb has a rating of 240 V,
60 W. Determine:
(a) The amount of current a bulb
filament would carry when
switched ON.
(b) The resistance of the bulb
filament.
7. In a car electrical system, the battery
of an emf of 12.0 V and internal
resistance r of 0.05  is connected
across a 12 V, 48 W headlight and a
starter motor of resistance 0.12 
as shown in Figure 2.40.
Student’s Book Form One
25/10/2025 10:26