Question

A TV set having a power rating of $200\,W$ operates for $5$ hours a day. What is the cost of electrical energy required to operate it for a period of $30$ days? The rate of electrical energy is Rs.3.40 per kWh.
A. Rs. 680
B. Rs. 17
C. Rs. 600
D. Rs. 102

Answer 1

Hint:The quantity of energy transported or transformed per unit time is referred to as power in physics. The watt, which is equal to one joule per second in the International System of Units, is the unit of power. Power is also referred to as activity in earlier texts. A scalar quantity is power. This is a concept that we utilise in to solve this problem.

Formula used:
$\text{Energy = Power }\!\!\times\!\!\text{ time}$

Complete step by step answer:
Electrical energy is the energy produced from electron mobility. Electrical energy is a term that is used to describe energy that has been transformed from electric potential energy. This energy is given via an electrical circuit that delivers a mix of electric current and electric potential (e.g., provided by an electric power utility).

This electric potential energy is no longer electric potential energy once it has been transformed to another sort of energy. The kilowatt hour (1 kWh = 3.6 MJ) is a unit of electrical energy that is calculated by multiplying the power in kilowatts by the operating time in hours. Now in the given question, power is 200 W, so when we convert it to Kilowatt we obtain $\dfrac{200}{1000}$=$\text{0}\text{.2kWh}$.
We know that, $\text{Energy = Power }\!\!\times\!\!\text{ time}$
Since time is 5 hours.
Energy becomes $E=0.2\times 5$
$\Rightarrow \text{E=1kWh}$
Suppose when we calculate It for 30 days
$\text{Energy = 1 x 30 = 30kWh}$
Rate being Rs. 3.40 per kWh.
For 30 kWh we get $30\times 3.40=\text{Rs}.102$

Hence option D is correct.

Note:Sometimes students try to convert hours to seconds which is absolutely wrong because it is clearly given in the unit as kWh (kilo – watt – hour). So we can solve the problem as such. Energy is the quantitative quality that must be supplied to a body or physical system in order to perform work on it or to heat it, according to physics.