Chapter 34, Problem 69A

A microwave oven is marked '120 V, 1100 w.'

a. How much current does the oven draw?

b. To heat 380 g of $20°\text{C}$ water to $86°\text{C}$ show that you should set the timer for at least 95 s.

To determine

To find: The magnitude of current

Explanation of Solution

The magnitude of current is

  $I=\frac{P}{V}=\frac{120\text{V}}{1100\text{W}}=0.109\text{A}$

To determine

To show: One should set timer for 95 s

Explanation of Solution

Specific heat capacity of water is $c=4.18\frac{\text{J}}{\text{g}{}^{\text{o}}\text{C}}$

  $\begin{array}{c}\text{Time}=\frac{\text{Heat}}{\text{Power}}\\ =\frac{mc\Delta T}{P}\\ =\frac{\left(380\text{g}\right)\left(4.18\frac{\text{J}}{\text{g}{}^{\text{o}}\text{C}}\right)\left(86{}^{\text{o}}\text{C}-20{}^{\text{o}}\text{C}\right)}{1100\text{W}}\\ =95.3\text{s}\end{array}$

Therefore set timer for 95 s