Grade 12 : Physics - Current Electricity (Set 2)

Question 1

A constant electric current of 5.0 A flows through a copper wire connected to a laboratory power supply.

Calculate the total charge that passes through a cross-section of the wire in 2.0 minutes.

Accepted Answer

B) 600 C

Answer

A) 300 C

Answer

C) 1200 C

Answer

D) 100 C

Question 2

A metallic conductor of cross-sectional area $1.0 imes 10^{-6}m^2$ carries a current of 1.36 A. The free electron density is $8.5 imes 10^{28}m^{-3}$ and electron charge is $e = 1.6 imes 10^{-19} ext{ C}$.

What is the drift velocity of the electrons in the conductor?

Accepted Answer

A) $1.0 	imes 10^{-4}m/s$

Answer

B) $2.5 	imes 10^{-3}m/s$

Answer

C) $5.0 	imes 10^{-2}m/s$

Answer

D) $1.0 	imes 10^{-5}m/s$

Question 3

A copper wire of length 10 m has a uniform cross-sectional area of $2.0 imes 10^{-6}m^2$. The resistivity of copper is $1.7 imes 10^{-8}\ \Omega\cdotm$.

Calculate the electrical resistance of the wire.

Accepted Answer

B) $0.085\ \Omega$

Answer

A) $0.17\ \Omega$

Answer

C) $0.34\ \Omega$

Answer

D) $0.0425\ \Omega$

Question 4

A metallic resistor has a resistance of $10.0\ \Omega$ at $0^\circ ext{C}$. The temperature coefficient of resistance for the material is $\alpha = 0.004\^\circ ext{C}^{-1}$.

What will be its resistance when heated to $50^\circ ext{C}$?

Accepted Answer

C) $12.0\ \Omega$

Answer

A) $10.5\ \Omega$

Answer

B) $11.0\ \Omega$

Answer

D) $15.0\ \Omega$

Question 5

Electrons inside a conductor experience a drift velocity of $4.0 imes 10^{-4}m/s$ under an applied uniform electric field of 100 V/m.

Determine the mobility $\mu$ of the electrons.

Accepted Answer

A) $4.0 	imes 10^{-6}m^2/(	ext{V}\cdot	ext{s})$

Answer

B) $2.5 	imes 10^{-5}m^2/(	ext{V}\cdot	ext{s})$

Answer

C) $8.0 	imes 10^{-6}m^2/(	ext{V}\cdot	ext{s})$

Answer

D) $1.0 	imes 10^{-4}m^2/(	ext{V}\cdot	ext{s})$

Question 6

Three resistors $R_1 = 4\ \Omega$, $R_2 = 6\ \Omega$, and $R_3 = 10\ \Omega$ are connected in series across an ideal 40 V battery.

Find the total current supplied by the battery.

Accepted Answer

B) 2.0 A

Answer

A) 1.0 A

Answer

C) 4.0 A

Answer

D) 5.0 A

Question 7

Two resistors of resistances $10\ \Omega$ and $15\ \Omega$ are connected in parallel combination.

Calculate the equivalent resistance of the combination.

Accepted Answer

C) $6.0\ \Omega$

Answer

A) $25\ \Omega$

Answer

B) $12.5\ \Omega$

Answer

D) $4.0\ \Omega$

Question 8

A cell of EMF $E = 12 ext{ V}$ and internal resistance $r = 1.0\ \Omega$ is connected to an external load resistor $R = 5.0\ \Omega$.

What is the terminal potential difference across the cell?

Accepted Answer

B) 10.0 V

Answer

A) 12.0 V

Answer

C) 8.0 V

Answer

D) 2.0 V

Question 9

Four identical cells, each of EMF 1.5 V and internal resistance $0.5\ \Omega$, are connected in series to an external load of $10.0\ \Omega$.

Find the current flowing through the circuit.

Accepted Answer

B) 0.50 A

Answer

A) 0.25 A

Answer

C) 1.00 A

Answer

D) 2.00 A

Question 10

Three identical cells, each having EMF 2.0 V and internal resistance $3.0\ \Omega$, are connected in parallel across an external resistor of $3.0\ \Omega$.

Calculate the current through the external resistor.

Accepted Answer

A) 0.50 A

Answer

B) 1.00 A

Answer

C) 1.50 A

Answer

D) 2.00 A

Question 11

At a circuit junction J, currents of 3.0 A and 4.0 A enter the junction through two wires. Two wires leave the junction; one carries a current of 2.0 A and the other carries unknown current $I$.

Applying Kirchhoff's Current Law, what is the magnitude of current $I$?

Accepted Answer

C) 5.0 A

Answer

A) 1.0 A

Answer

B) 3.0 A

Answer

D) 7.0 A

Question 12

A simple closed loop circuit consists of a 12 V battery in series with two resistors of $2.0\ \Omega$ and $4.0\ \Omega$.

Using Kirchhoff's Voltage Law, find the potential drop across the $4.0\ \Omega$ resistor.

Accepted Answer

C) 8.0 V

Answer

A) 4.0 V

Answer

B) 6.0 V

Answer

D) 12.0 V

Question 13

In a Wheatstone bridge circuit, the four arms have resistances $P = 4\ \Omega$, $Q = 8\ \Omega$, $R = 5\ \Omega$, and $S = X\ \Omega$.

If the bridge is balanced, what is the value of the unknown resistance $X$?

Accepted Answer

C) $10.0\ \Omega$

Answer

A) $5.0\ \Omega$

Answer

B) $8.0\ \Omega$

Answer

D) $16.0\ \Omega$

Question 14

In a meter bridge experiment, an unknown resistor $X$ is placed in the left gap and a standard resistor $Y = 15.0\ \Omega$ is placed in the right gap. The null point is obtained at $l = 40.0cm$ from the left end.

Calculate the value of the unknown resistance $X$.

Accepted Answer

A) $10.0\ \Omega$

Answer

B) $15.0\ \Omega$

Answer

C) $22.5\ \Omega$

Answer

D) $30.0\ \Omega$

Question 15

A potentiometer wire is used to compare the EMFs of two primary cells. Cell 1 of EMF $E_1 = 1.5 ext{ V}$ yields a balancing length of 60.0 cm. Cell 2 gives a balancing length of 80.0 cm.

Determine the EMF $E_2$ of the second cell.

Accepted Answer

C) 2.00 V

Answer

A) 1.125 V

Answer

B) 1.80 V

Answer

D) 2.50 V

Question 16

When determining the internal resistance of a cell using a potentiometer, the balance length is 75.0 cm on open circuit. When a resistor $R = 10.0\ \Omega$ is connected across the cell, the balance length reduces to 60.0 cm.

Calculate the internal resistance $r$ of the cell.

Accepted Answer

C) $2.5\ \Omega$

Answer

A) $1.5\ \Omega$

Answer

B) $2.0\ \Omega$

Answer

D) $3.0\ \Omega$

Question 17

An electric lamp rated 100 W operates continuously at its rated voltage of 220 V for a duration of 5.0 hours.

What is the electrical energy consumed by the lamp in kilowatt-hours (kWh)?

Accepted Answer

B) 0.50 kWh

Answer

A) 0.10 kWh

Answer

C) 1.00 kWh

Answer

D) 2.00 kWh

Question 18

A constant electric current of 2.0 A passes through a resistor of resistance $5.0\ \Omega$ for a time interval of 10.0 seconds.

Calculate the total heat energy produced in the resistor (Joule heating).

Accepted Answer

B) 200 J

Answer

A) 100 J

Answer

C) 400 J

Answer

D) 500 J

Question 19

A household operates a 60 W electrical appliance for 10 hours per day throughout a 30 day month. Electricity costs $\0.10 per $kWh$.

What is the total cost of operating this appliance for the month?

Accepted Answer

B) $\1.80

Answer

A) $\0.90

Answer

C) $\3.60

Answer

D) $\5.40

Question 20

Inside a conducting material, a uniform electric current density of $j = 2.0 imes 10^6 ext{ A/m}^2$ is established. The electrical conductivity of the material is $\sigma = 5.0 imes 10^7 ext{ S/m}$.

Using vector Ohm's Law ($j = \sigma E$), find the electric field magnitude $E$ inside the conductor.

Accepted Answer

A) 0.04 V/m

Answer

B) 0.25 V/m

Answer

C) 0.40 V/m

Answer

D) 2.50 V/m