Question

name introduction to engineering homework: ohms law
problems

1. what is the voltage across a 220 ω resistor if the current through it is 5.6 ma?
2. at starting, what is the current drain on a 12 v battery if the resistance of the starting motor is 40 mω?
3. if a voltmeter has an internal resistance of 50 kω, find the current through the meter when it reads 120 v.
4. if a refrigerator draws 2.2 a at 120 v, what is its resistance?
5. if a clock has an internal resistance 8 kω, find the current through the clock if it is plugged into a 120 v outlet?
6. a washing machine is rated at 4.2 a at 120 v. what is its internal resistance?
7. the input current to a transistor is 20 μa. if the applied (input) voltage is 24 mv, determine the input resistance of the transistor.

Explanation:

Step1: Recall Ohm's Law

Ohm's Law is $V = IR$, where $V$ is voltage, $I$ is current, and $R$ is resistance. We can also express it as $I=\frac{V}{R}$ and $R = \frac{V}{I}$ for different - problem - solving needs.

Step2: Solve problem 2

Given $V = 12\ V$ and $R=40\times10^{- 3}\ \Omega$. Using $I=\frac{V}{R}$, we substitute the values: $I=\frac{12\ V}{40\times10^{-3}\ \Omega}=300\ A$.

Step3: Solve problem 5

Given $V = 120\ V$ and $R = 8\times10^{3}\ \Omega$. Using $I=\frac{V}{R}$, we substitute the values: $I=\frac{120\ V}{8\times10^{3}\ \Omega}=0.015\ A = 15\ mA$.

Step4: Solve problem 7

Given $I = 20\times10^{-6}\ A$ and $V=24\times10^{-3}\ V$. Using $R=\frac{V}{I}$, we substitute the values: $R=\frac{24\times10^{-3}\ V}{20\times10^{-6}\ A}=1200\ \Omega = 1.2\ k\Omega$.

Answer:

Problem 2: $300\ A$
Problem 5: $15\ mA$
Problem 7: $1.2\ k\Omega$