Question

critical thinking

1. infer toasters and space heaters heat up when current flows through them. do they use material with low resistance or high resistance?

Explanation:

Step1: Recall the formula for heat generated

The formula for heat generated \( H \) in a conductor is \( H = I^{2}Rt \) (where \( I \) is current, \( R \) is resistance, \( t \) is time).

Step2: Analyze the requirement for heating devices

For toasters and space - heaters, we want a significant amount of heat to be generated. Given a constant voltage \( V \) (since they are connected to a power supply of fixed voltage), using \( I=\frac{V}{R} \), we can rewrite the heat formula as \( H=\frac{V^{2}t}{R} \) (by substituting \( I = \frac{V}{R} \) into \( H = I^{2}Rt \)).

Step3: Determine the resistance type

From \( H=\frac{V^{2}t}{R} \), for a large \( H \) (to generate enough heat), with \( V \) (voltage) and \( t \) (time of operation) being constant (for a given usage scenario), \( R \) (resistance) should be high. Because if \( R \) is high, the fraction \( \frac{V^{2}t}{R} \) will give a reasonable amount of heat. If \( R \) was low, for a fixed \( V \), the current \( I=\frac{V}{R} \) would be very high, which can cause over - heating of wires (not the heating element) and is a safety hazard (due to high power \( P = VI=\frac{V^{2}}{R}\)).

Answer:

They use material with high resistance.