Question

Which uses more energy, a 250 W TV set in 1hr or a 1200 W toaster in 10 minutes?

Answer 1

Hint: The rate of consumption or dissipation of energy with respect to time is called power i.e. $P\text{ }=\text{ }\dfrac{E}{t}$. With this formula of power, find the energy consumed by each appliance and compare to find which one is greater.


Complete step-by-step answer:
Let us first understand what the meaning of a 250W TV set and 1200W toaster is. 250W and 1200W is read as 250 watts and 1200 watts. Now, what is the meaning of watts? Watts is the unit of power. Power is the rate of consumption or dissipation of energy with time. It tells us the amount of energy taken or given in one unit time. Therefore, power (P) is the amount of energy consumed or dissipated (E) divided by the given time (t) for which the energy is consumed or dissipated i.e. $P\text{ }=\text{ }\dfrac{E}{t}$ .
We can rewrite the about equation as $E=Pt$ i.e. energy consumed or dissipated is the product of the power and the given time.
 Now, we can find the energy consumed by the TV set and the toaster.
Let the energy consumed by the TV set be E1. The power of consumption of energy is given to be P1=250W and the given time is ${{t}_{1}}=1hr=60\min =60\times 60\sec =3600\sec $.
Therefore, ${{E}_{1}}={{P}_{1}}{{t}_{1}}=250\times 3600=900000J$. The SI unit of energy is joules (J).
Let the energy consumed by the toaster be E2. The power of consumption of energy is given to be P2=1200W and the given time is ${{t}_{2}}=10\min =10\times 60\sec =600\sec $.
Therefore, ${{E}_{2}}={{P}_{2}}{{t}_{2}}=1200\times 600=720000J$.
As you can see, ${{E}_{1}}>{{E}_{2}}$, which means that the TV set consumes more energy than the toaster in the given time for both.

Additional Information: Joule is the SI unit of energy. There is one more unit of energy which is used for commercial purposes i.e. kilowatt-hour (KWh). 1 KWh is equal to the energy consumed by a device of 1 kW (1000W) power for 1hour. Suppose a device with power of 5kW i.e. 5000W, works for 2hours then the energy that it consumes in kWh is $E=5kW\times 2h=10kWh$. One kilowatt-hour is also called one unit. You may have seen in your home electric bills the energy consumption is written in units and it is charged according to these units. It is actually measured in kWh.

Note: Students may confuse between kW and kWh. Kilowatt is a unit of power and kilowatt-hour is a unit of energy. 1 kilowatt is equal to 1000watts i.e. $\text{1000}\dfrac{\text{joules}}{\text{seconds}}$.
One kilowatt-hour is equal to $1000w\text{atts }\!\!\times\!\!\text{ 60 }\!\!\times\!\!\text{ 60seonds =1000}\dfrac{\text{joules}}{\text{second}}\text{ }\!\!\times\!\!\text{ 3600seconds = 3}\text{.6 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{6}}}\text{joules}$