Question 1

A generator supplies 100 V to the primary coil of a transformer. The primary has 50 turns and the secondary has 500 turns. The secondary voltage is:
A) 1000 V
B) 500 V
C) 250 V
D) 100 V
E) 10 V

Accepted Answer

The secondary voltage can be calculated using the transformer equation: $V_s = V_p \times \frac{N_s}{N_p}$, where $V_s$ is the secondary voltage, $V_p$ is the primary voltage, $N_s$ is the number of turns in the secondary coil, and $N_p$ is the number of turns in the primary coil. Substituting the given values: $V_s = 100 V \times \frac{500}{50} = 1000 V$.

Question 2

The primary of a 3:1 step-up transformer is connected to a source and the secondary is connected to a resistor R. The power dissipated by R in this situation is P. If R is connected directly to the source it will dissipate a power of:
A) P/9
B) P/3
C) P
D) 3P
E) 9P

Accepted Answer

The answer of The primary of a 3:1 step-up transformer...

Question 3

A power transmission line carries 400A of current at a voltage of 765 kV. If the line has a resistance of 29 µΩ/m, what is the rate at which energy is being dissipated in 800 km of line?
A) 0 W
B) 3.7 kW
C) 310 kW
D) 3.7 MW
E) 310 MW

Accepted Answer

The answer of A power transmission line carries 400A of...

Question 4

The resistance of the primary coil of a well-designed, 1:10 step-down transformer is 1  $\Omega$. With the secondary circuit open, the primary is connected to a 12 V ac generator. The primary current is:
A) essentially zero
B) about 12 A
C) about 120 A
D) depends on the actual number of turns in the primary coil
E) depends on the core material

Accepted Answer

With the secondary circuit open, there is no load on the transformer, which means no current flows in the secondary coil. Hence, according to the transformer law, the primary current is also zero. The resistance of the primary coil does not affect the current in this case.

Question 5

A step-down transformer is used to:
A) increase the power
B) decrease the power
C) increase the voltage
D) decrease the voltage
E) change ac to dc

Accepted Answer

A step-down transformer is designed to decrease the voltage. It has more turns on the primary coil than the secondary coil, and so it induces a smaller voltage in the secondary coil than the voltage supplied to the primary coil. This is used, for example, in power distribution where high-voltage power lines are stepped down to lower voltages for domestic use.

Question 6

A source with an impedance of 100  $\Omega$ is connected to the primary coil of a transformer and a resistance R is connected to the secondary coil. If the transformer has 500 turns in its primary coil and 100 turns in its secondary coil the greatest power will be dissipated in the resistor if R =
A) 0  $\Omega$
B) 0.25  $\Omega$
C) 4.0  $\Omega$
D) 20  $\Omega$
E) 100 $\Omega$

Accepted Answer

The impedance seen by the secondary coil of the transformer is given by Z_sec = Z_prim*(N_sec/N_prim)^2, where Z_prim is the impedance of the source, N_sec is the number of turns in the secondary coil, and N_prim is the number of turns in the primary coil. Substituting the given values, we get Z_sec = 100*(100/500)^2 = 1 F1F1F1S1F1F1F10.
The power dissipated in the resistor is given by P = V^2/R, where V is the voltage across the resistor. The voltage across the resistor is given by V = I*R, where I is the current in the circuit. The current in the circuit is given by I = V/Z_sec. Substituting the values, we get I = 10 F1F1F1V1F1F1F1S1F1F1F11 = 10 F1F1F1A1. Therefore, the power dissipated in the resistor is P = (10 F1F1F1V1F1F1F1S1F1F1F11)^2/R = 1000/R. For maximum power dissipation in the resistor, we need to minimize R. Therefore, the answer is the smallest value of R given, which is 4.0 F1F1F1S1F1F1F10.

Question 7

The primary of an ideal transformer has 100 turns and the secondary has 600 turns. Then:
A) the power in the primary circuit is less than that in the secondary circuit
B) the currents in the two circuits are the same
C) the voltages in the two circuits are the same
D) the primary current is six times the secondary current
E) the frequency in the secondary circuit is six times that in the primary circuit

Accepted Answer

The primary current is six times the secondary current due to the transformer's turn ratio of 1:6 (100 turns to 600 turns), which inversely affects the current.

Question 8

In an ideal 1:8 step-down transformer, the primary power is 10 kW and the secondary current is 25 A. The primary voltage is:
A) 25,600 V
B) 3200 V
C) 400 V
D) 50 V
E) 6.25 V

Accepted Answer

Power in primary = Power in secondary
10 kW = Vp * Ip
Ip = Is/8 = 25/8 = 3.125 A
Vp = 10,000 / 3.125 = 3200 V

Quiz 31: Electromagnetic Oscillations and Alternating Current

A generator supplies 100 V to the primary coil of a transformer. The primary has 50 turns and the secondary has 500 turns. The secondary voltage is:

The primary of a 3:1 step-up transformer is connected to a source and the secondary is connected to a resistor R. The power dissipated by R in this situation is P. If R is connected directly to the source it will dissipate a power of:

A power transmission line carries 400A of current at a voltage of 765 kV. If the line has a resistance of 29 µΩ/m, what is the rate at which energy is being dissipated in 800 km of line?

The resistance of the primary coil of a well-designed, 1:10 step-down transformer is 1 $\Omega$ . With the secondary circuit open, the primary is connected to a 12 V ac generator. The primary current is:

A step-down transformer is used to:

A source with an impedance of 100 $\Omega$ is connected to the primary coil of a transformer and a resistance R is connected to the secondary coil. If the transformer has 500 turns in its primary coil and 100 turns in its secondary coil the greatest power will be dissipated in the resistor if R =

The primary of an ideal transformer has 100 turns and the secondary has 600 turns. Then:

In an ideal 1:8 step-down transformer, the primary power is 10 kW and the secondary current is 25 A. The primary voltage is: