Chapter 34, Problem 70A

A typical car headlight may put out 50 watts at 12 volts.

a. Show that 4.2 A is drawn by the headlight.

b. How many electrons pass through the bulb filament each second?

To determine

To show: The current from headlight is 4.2 A

Explanation of Solution

The current from headlight is $I=\frac{P}{V}=\frac{50\text{W}}{12\text{V}}\approx 4.2\text{A}$

To determine

To find: the number of electron pass from bulb filament

Explanation of Solution

Magnitude of Charge on electron, $q=1.6\times {10}^{-19}\text{C}$

The number of electron pass from bulb filament in time, $t=1\text{s}$

  $n=\frac{It}{q}=\frac{\left(4.2\text{A}\right)\left(1\text{s}\right)}{1.6\times {10}^{-19}\text{C}}=2.65\times {10}^{19}\text{electrons}$