Question 1

An electric motor produces 2.0 hp in a V_rms = 120 V circuit.What is I_rms for this motor? (1 hp = 746 W) A) 12 A B) 6.2 A C) 0.62 A D) 1.6 A

Accepted Answer

The answer of An electric motor produces 2.0 hp in...

Question 2

An AC power generator produces 100 A (rms)at 3600 V.The voltage is stepped up to 100,000 V by an ideal transformer,and the energy transmitted through a long-distance power line with a total resistance of 100 Ω.What is the rms current in the long-distance line?
A) 3.6 A
B) 1.0 A
C) 1000 A
D) 1.8 A

Accepted Answer

The power on both sides of an ideal transformer is the same. The power on the primary side is P = IV = 100 A * 3600 V = 360,000 W. On the secondary side, with a voltage of 100,000 V, the current is I = P/V = 360,000 W / 100,000 V = 3.6 A.

Question 3

A transformer consists of a 1000-turn primary coil and a 4000-turn secondary coil.If the current in the secondary is 3.00 A,what is the primary current?
A) 6.00 A
B) 0.750 A
C) 48.0 A
D) 12.0 A

Accepted Answer

The answer of A transformer consists of a 1000-turn primary...

Question 4

A transformer is to be designed to increase the 30 kV (rms)output of a generator to the transmission line voltage of 345 kV (rms).If the primary winding has 60 turns,how many turns must the secondary have?
A) 57
B) 6900
C) 690
D) 11

Accepted Answer

The turn ratio of the transformer can be calculated as follows:
turns ratio = V2/V1
where V2 = 345 kV and V1 = 30 kV
turns ratio = 345/30 = 11.5
Since the primary winding has 60 turns, the secondary winding must have:
Secondary turns = turns ratio * primary turns
Secondary turns = 11.5 * 60 = 690
Therefore, the correct answer is C) 690.

Question 5

An AC power generator produces 25 A (rms)at 3600 V.The energy is transmitted through a long-distance power line,which has a total resistance of 50 Ω.What percentage of the power delivered by the generator is dissipated as heat in the long-distance line if a step-up transformer is not used?
A) 69%
B) 35%
C) 0.09%
D) 1.8%

Accepted Answer

To find the percentage of the power dissipated as heat in the long-distance power line, we need to calculate the power delivered and the power dissipated.

The power delivered by the generator is given by:

P = VI = (25 A) x (3600 V) = 90,000 W

The power dissipated in the long-distance power line is given by:

Pdiss = I^2R = (25 A)^2 x (50 Ω) = 31,250 W

The percentage of the power dissipated as heat in the long-distance line is:

( Pdiss / P ) x 100% = ( 31,250 W / 90,000 W ) x 100% = 34.7% ≈ 35%

Therefore, the answer is B.

Question 6

The primary winding of an electric train transformer has 200 turns,and the secondary has 50.If the input voltage is 120 V(rms),what is the output voltage?
A) 30 V
B) 15 V
C) 10 V
D) 480 V

Accepted Answer

The output voltage can be calculated using the transformer turns ratio formula: V_secondary = (N_secondary / N_primary) * V_primary. Here, V_secondary = (50/200) * 120 V = 30 V.

Question 7

Transmitting power at high voltage,e.g. ,400,000 V,reduces the power loss for transmission lines.But such a voltage would destroy electrical devices in household use.How then can such 400,000 V electricity be used in a normal house?
A) The ground prongs on household plugs reduce the voltage to 120 V.
B) Before reaching households,transformers are used to reduce the voltage appropriately.
C) No matter the incoming voltage,a 120-V device only lets 120 V in.
D) The 400,000 V is just theoretical;long distance transmission lines actually use 120 V.

Accepted Answer

Before the electricity reaches households, it is passed through step-down transformers that reduce the voltage to an appropriate level for household use (usually 120 V in the United States). This allows for the efficient transmission of electricity over long distances without damaging household devices.

Question 8

An electric motor produces 2.0 hp in a V_rms = 120 V circuit.Using 1 hp = 746 W,how long would it take this motor to do 1.0 kWh of work? A) 0.67 min B) 0.67 h C) 1.3 min D) 1.3 h

Accepted Answer

First, convert 2.0 hp to watts: 
2.0 hp x 746 W/hp = 1492 W

Next, determine how long it takes for the motor to do 1.0 kWh of work: 
1.0 kWh x 1000 Wh/kWh = 1000 Wh 
1000 Wh ÷ 1492 W = 0.67 h

Therefore, the answer is B) 0.67 h.

Question 9

In an AC circuit operating at a frequency where the phase angle with respect to the current is 30°,what happens to the phase angle if the capacitance of the circuit is increased?
A) It increases.
B) It decreases.
C) nothing
D) It decreases and can become zero.

Accepted Answer

If the capacitance of an AC circuit is increased, the phase angle with respect to the current increases. This is due to the fact that the reactance of the capacitor (1/ωC) decreases with increasing capacitance, resulting in a higher impedance and a larger phase difference between voltage and current. Therefore, the answer is A - it increases.

Quiz 22: Reflection and Refraction of Light: Part A

An electric motor produces 2.0 hp in a V_rms = 120 V circuit.What is I_rms for this motor? (1 hp = 746 W)

An AC power generator produces 100 A (rms) at 3600 V.The voltage is stepped up to 100,000 V by an ideal transformer,and the energy transmitted through a long-distance power line with a total resistance of 100 Ω.What is the rms current in the long-distance line?

A transformer consists of a 1000-turn primary coil and a 4000-turn secondary coil.If the current in the secondary is 3.00 A,what is the primary current?

A transformer is to be designed to increase the 30 kV (rms) output of a generator to the transmission line voltage of 345 kV (rms) .If the primary winding has 60 turns,how many turns must the secondary have?

An AC power generator produces 25 A (rms) at 3600 V.The energy is transmitted through a long-distance power line,which has a total resistance of 50 Ω.What percentage of the power delivered by the generator is dissipated as heat in the long-distance line if a step-up transformer is not used?

The primary winding of an electric train transformer has 200 turns,and the secondary has 50.If the input voltage is 120 V(rms) ,what is the output voltage?

Transmitting power at high voltage,e.g. ,400,000 V,reduces the power loss for transmission lines.But such a voltage would destroy electrical devices in household use.How then can such 400,000 V electricity be used in a normal house?

An electric motor produces 2.0 hp in a V_rms = 120 V circuit.Using 1 hp = 746 W,how long would it take this motor to do 1.0 kWh of work?

In an AC circuit operating at a frequency where the phase angle with respect to the current is 30°,what happens to the phase angle if the capacitance of the circuit is increased?