Question

A torch bulb is rated 5V and 500mA calculate its 1) power 2) resistance and 3) energy consumed when it is lighted for 4 hours.

Answer 1

In this question, we will directly use the expressions to find power, resistance and energy to get our result. Further, by substituting the given values in each expression will give us the required result. Also, we will study the basics of power, energy and resistance, for our better understanding.

Formula used:
$P = V \times I$
$R = \dfrac{V}{I}$
$E = P \times t$

Complete step by step solution:
As we know power P is given as:
$P = V \times I$

Now, we will substitute the given values in above equation as:
$P = 5 \times 500 \times {10^{ - 3}}W$
$\Rightarrow P = 2.5W$

From Ohm’s law, resistance R is given as:
$R = \dfrac{V}{I}$

Now, we will substitute the given values in above equation to find the resistance as:
$R = \dfrac{5}{{500 \times {{10}^{ - 3}}}}$
$\Rightarrow R = 10\Omega$

Energy consumed by the bulb for 4 hours is given by:
$E = P \times t$

Now, we will substitute the given values in above equation to find the energy consumed as:
\eqalign{ & E = 2.5 \times 4 \cr & \therefore E = 10J \cr}

Therefore, we get all the required results to our question.

Additional information:
$\bullet$ We should also know about the power. It is the amount of energy transferred or converted per unit time. In the International System or S.I Unit of power is the watt. Power is a scalar quantity, which means it has only magnitude not direction.
$\bullet$ We also know that the electrical resistance of a circuit or device is defined as the ratio of the applied voltage V to the current I which flows through it.
$\bullet$ As we know that energy is defined as the ability to do work. Energy can be found in many things and can take different forms, like-kinetic energy is the energy of motion, and potential energy is energy due to an object's position or structure. Total energy of a system is given by the sum of kinetic energy and potential energy.

Note:
We should remember that the laws of conservation of energy can never be violated in any case. According to the law of conservation of energy, energy can neither be created nor be destroyed; rather it can only be transferred from one form to another.