Chapter 22, Problem 4STP

To determine

To choose: The correct option.

Answer to Problem 4STP

The correct option is (D), $\text{4}\text{.1}\times {10}^2\text{ J}$

Explanation of Solution

Given:

A flashlight with a voltage of 4.5-V and current of 0.50 A is used for duration of 3.0 min

Formula used:

The energy transformed in the bulb, E can be expressed in terms of the power dissipation and the time for which power is drawn, t, as

  $E=Pt$

The power drawn by the bulb is a function of current I and voltage drop across it, V, which can be expressed as,

  $P=VI$

Calculation:

Substituting the voltage and resistance value, the power can be obtained as,

  $\begin{array}{c}P=4.5\times 0.5\\ =2.25\text{ W}\end{array}$

Now, substituting the value of power and time, the energy can be calculated as,

  $\begin{array}{c}E=2.25\times 3.0\times 60\\ =4.05\times {10}^2\text{ W/s}\\ \text{=4}\text{.1}\times {10}^2\text{ J}\end{array}$

Conclusion:

Therefore, the correct option representing the energy delivered to the bulb is (D), $\text{4}\text{.1}\times {10}^2\text{ J}$