Question

ii. practice problems
for each problem, draw a picture of the simple circuit and then solve for the missing quantity.

1. what resistance is needed to restrict a 9 v battery to a current of 0.5 a?
2. calculate the current in a toaster that has a heating element of 30 ω when plugged into an ordinary wall outlet at 120 v?

Explanation:

Step1: Recall Ohm's Law

Ohm's Law is $V = IR$, rearranged for resistance: $R = \frac{V}{I}$

Step2: Solve Problem 3

Substitute $V=9\ \text{V}$, $I=0.5\ \text{A}$
$R = \frac{9}{0.5} = 18\ \Omega$

Step3: Rearrange Ohm's Law for current

$I = \frac{V}{R}$

Step4: Solve Problem 4

Substitute $V=120\ \text{V}$, $R=30\ \Omega$
$I = \frac{120}{30} = 4\ \text{A}$

Answer:

1. The required resistance is $18\ \Omega$
2. The current in the toaster is $4\ \text{A}$

(Note: For circuit diagrams:

• Problem 3: A 9V battery connected in series with a 18Ω resistor and an ammeter reading 0.5A.
• Problem 4: A 120V wall outlet connected in series with a 30Ω heating element and an ammeter reading 4A.)