Question

A. What is the resistance of an electric frying pan that draws 12 amperes of current when connected to a 120 V circuit?

B. If your skin were very moist so that your resistance was only 1000 ohms, and you touched the terminals of a 24 V battery, how much current would you draw?

C. A certain battery has an 18.0 V EMF and an internal resistance of 0.015 Ω. Find the current, terminal voltage, and power dissipated by a load with 0.500 Ω.

with solution, thank you!

Answer 1

a) According to the Ohm's law:

$$V = IR$$

where $R$ is the resistance, $I = 12A$ is the current and $V = 120V$ is the voltage. Thus, obtain:

$$R = \dfrac{V}{I} = 10\Omega$$

b) Similarly:

$$I = \dfrac{V}{R} = \dfrac{24V}{1000\Omega} = 0.024A$$

c) The current in this case is (see https://courses.lumenlearning.com/physics/chapter/21-2-electromotive-force-terminal-voltage/):

$$I = \dfrac{emf}{R_{load} +r}$$

where $emf = 18V, R_{load}=0.5\Omega, r=0.015\Omega$. Thus, obtain:

$$I = \dfrac{18V}{0.5\Omega +0.015\Omega} \approx 35.0A$$

The terminal voltage:

$$V = emf-Ir = 18V-35A\cdot 0.015\Omega \approx 17.5V$$

The power:

$$P = I^2R_{load} = (35.0A)^2\cdot 0.5\Omega \approx 611W$$