Question

q.4. two types of electrical current exist: direct current (dc) and alternating current (ac). these types of electric currents are shown in the images below. label them correctly.
definition: the type of electric current that regularly reverses its direction.
examples:

• washing machines, refrigerators

definition: the type of electric current that flows in a single direction.
examples:

• batteries, solar panels

q.5. what is the name of a device that contains a short piece of metal that melts quickly if an excessive current flows through it?
a) voltmeter b) battery c) switch d) fuse

q.6. which of the following laws states that the current is directly proportional to the voltage and inversely proportional to the resistance?
a) ohms law b) newtons law
c) joules law d) daltons law

q.7. what current flows through a bulb plugged into a 12 volt circuit if it has a resistance of 4 ohms?
a) 2 a b) 3 a
c) 4 a d) 48 a

q.8. what is the resistance of a bulb carrying a current of 8 a when connected to a 120 v supply?
a) 5 ω b) 10 ω
c) 15 ω d) 20 ω

q.9. what is the correct equation for calculating electrical power?
a) electrical power (p) = voltage (v) ÷ current (i)
b) electrical power (p) = voltage (v) x current (i)
c) electrical power (p) = voltage (v) ÷ resistance (r)
d) electrical power (p) = voltage (v) x resistance (r)

Explanation:

Q.4

Step1: Recall AC and DC definitions

AC reverses direction, DC flows in one - direction. So the left - hand image (reversing direction) is AC, the right - hand image (single direction) is DC.

Q.5

Step1: Know function of electrical devices

A fuse contains a metal piece that melts when excessive current flows. So the answer is d) Fuse.

Q.6

Step1: Recall electrical laws

Ohm's Law states current is proportional to voltage and inversely proportional to resistance. So the answer is a) Ohm's Law.

Q.7

Step1: Apply Ohm's Law ($I=\frac{V}{R}$)

Given $V = 12$ V and $R = 4$ $\Omega$, then $I=\frac{12}{4}=3$ A. So the answer is b) 3 A.

Q.8

Step1: Rearrange Ohm's Law ($R=\frac{V}{I}$)

Given $V = 120$ V and $I = 8$ A, then $R=\frac{120}{8}=15$ $\Omega$. So the answer is c) 15 $\Omega$.

Q.9

Step1: Recall power formula

The formula for electrical power is $P = V\times I$. So the answer is b) Electrical Power $(P)=$ Voltage $(V)\times$ Current $(I)$.

Answer:

Q.4: Left: Alternating current (AC), Right: Direct current (DC)
Q.5: d) Fuse
Q.6: a) Ohm's Law
Q.7: b) 3 A
Q.8: c) 15 $\Omega$
Q.9: b) Electrical Power $(P)=$ Voltage $(V)\times$ Current $(I)$