1. A 220 V – 5 A electric lamp is used for 30 minutes. How much energy does it require?
Solution :
Voltage (V) = 220 Volt
Electric current (I) = 5 Ampere
Time (t) = 30 minutes = 30 x 60 seconds = 1800 seconds
Electric power (P) :
P = V I = (220 Volt)(5 Ampere) = 1100 Volt Ampere = 1100 Watt = 1100 Joule/second
Electric energy = Electric power x time = (1100 Joule/second)(1800 second)
Electric energy = 1,980,000 Joule = 1,980 kiloJoule
[irp]
2. A 220 V – 60 W solder is used for 4 minutes. How much energy does it require.
Known :
Power (P) = 60 Watt = 60 Joule/second
Voltage (V) = 220 Volt
Time (t) = 4 minutes = 4 x 60 seconds = 240 seconds
Wanted: Electric power
Solution :
220 Volt – 60 Watt means the electric solder works well if the potential difference or voltage is 220 volts and has a power of 60 Watt = 60 Joule/second, means that electric solder using the energy of 60 Joules per second.
Electric energy = electric power x time interval = (60 Joule/second)(240 second) = 14,400 Joule.
[irp]
3. The energy used by the iron for 1 minute is 33 kJ, at a voltage of 220 volts. How large the current is in the iron.
Known :
Time interval (t) = 1 minute = 60 seconds
Energy (W) = 33 kiloJoule = 33,000 Joule
Voltage (V) = 220 Volt
Wanted : Electric current (I)
Solution :
Electrical power is the electrical energy used during a certain time interval.
P = W / t = 33,000 Joule / 60 seconds
P = 550 Watt
Electric current :
I = P / V = 550 / 220 = 2.5 Ampere
[irp]
4. Someone watches TV on average 6 hours each day. The TV is connected to a 220 Volt voltage so that the electric current flows through the TV is 0.5 Amperes. If the electric company charges $0.092 per kWh, then the cost of using electric energy for TV for 1 month (30 days) is…
Known :
Time interval = 6 hours x 30 = 180 hours
Voltage (V) = 220 Volt
Electric current (I) = 0.5 Ampere
Wanted : The cost per month
Solution :
Power of TV :
P = V I = (220 Volt)(0.5 Ampere) = 110 Volt Ampere = 110 Watt
Electric energy = electric power x time interval
Electric energy of TV = 110 Watt x 180 hours = 19800 Watt hours = 19.8 kilo Watt hours = 19.8 kilo Watt hours = 19.8 kWh
The cost of using electric energy for TV during 1 month :
19.8 kWh x $ 0.092 / kWh = $ 1.8216
[irp]
5. In a house there are 4 lamps 20 Watt, 2 lamps 10 Watt, 3 lamps 40 Watt, are used 5 hours every day. If the electric company charge 0.092 per kWh, then the cost of using electric energy during 1 month (30 days) is ….
Known :
4 lamps 20 Watt = 4 x 20 Watt = 80 Watt
2 lamps 10 Watt = 2 x 10 Watt = 20 Watt
3 lamps 40 Watt = 3 x 40 Watt = 120 Watt
Total power (W) = 80 Watt + 20 Watt + 120 Watt = 220 Watt
Time interval (t) = 5 hours x 30 = 150 hours
Wanted : The cost of using electric energy during 1 month (30 days)
Solution :
Electric energy = electric power x time interval = 220 Watt x 150 hours = 33,000 Watt hour = 33 kilo Watt hour = 33 kilo Watt hour = 33 kWh
The cost of using electric energy during 1 month (30 days)
(33 kWh) ( 0.092 / kWh) = $ 3.036
