Chapter 18, Problem 7P

(a)

To determine

The current in the element when it is connected to $\text{240}\text{V}$ .

Answer to Problem 7P

  $\text{25}\text{A}$

Explanation of Solution

Given:

Voltage, $\text{V=}\text{240}\text{V}$ and resistance, $\text{R= 9}\text{.6}\text{Ω}$ .

Formula used:

From the Ohm’s law,

The relation between resistance, voltage and current

  $\text{V=IR}$

Where $V=$ voltage, $I=$ current, $R=$ resistance.

After rearranging this expression, $\text{I=}\frac{\text{V}}{\text{R}}$

Calculation:

Relation between resistance, voltage and current is $\text{I=}\frac{\text{V}}{\text{R}}$

Substituting the values in formula $\text{I=}\frac{\text{V}}{\text{R}}$

  $\text{=}\frac{\text{240}\text{V}}{\text{9}\text{.6}\text{Ω}}$

  $\text{=25}\text{A}$

Conclusion:

The current in element of cloth dryer is $\text{25}\text{A}$ .

(b)

To determine

The charge passes through the element in $\text{50}\text{min}$ .

Answer to Problem 7P

  $\text{7}\text{.5}\text{×}{\text{10}}^{\text{4}}\text{C}$

Explanation of Solution

Given:

Voltage, $\text{V=}\text{240}\text{V}$ and resistance, $\text{R= 9}\text{.6}\text{Ω}$ and time, $\text{t=50}\text{min}$ .

Formula used:

The current is given by

  $\text{I}\text{=}\frac{\Delta \text{Q}}{\Delta \text{t}}$

For the calculation of charge $\Delta \text{Q}\text{=}\text{I}\Delta \text{t}$

Where, $I=$ current, $\Delta Q=$ amount of charge (change), and $\Delta t=$ change in time.

Calculation:

Substituting the values in the formula, $\Delta \text{Q}\text{=}\text{I}\Delta \text{t}$

  $\text{= 25}\text{A×50}\text{min}\text{×60}\text{s}$

  $\text{=}\text{7}\text{.5}\text{×}{\text{10}}^{\text{4}}\text{C}$

Conclusion:

The charge passes through the element is $\text{7}\text{.5}\text{×}{\text{10}}^{\text{4}}\text{C}$ .