Question 1

You leave your 120-W lightbulb on in your room by mistake while you are at school for 8.5 hours. If the price of electrical energy is $0.085 per kilowatt-hour, how much did it cost you?

Accepted Answer

First, we need to convert the wattage of the lightbulb to kilowatts:
120 W = 0.12 kW

Next, we can calculate the energy used by multiplying the power (in kW) by the time (in hours):
0.12 kW x 8.5 hours = 1.02 kWh

Finally, we can find the cost by multiplying the energy used by the cost per kilowatt-hour:
1.02 kWh x $0.085/kWh = $0.087

Therefore, the cost is $0.087, which corresponds to choice D.

Question 2

The curve that best represents the power loss in a resistor is

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Question 3

If it takes you 5 minutes to dry your hair using a 1200-W hair dryer plugged into a 120-V power outlet, how many coulombs of charge pass through your hair dryer?

Accepted Answer

The power (P) is 1200 W and the voltage (V) is 120 V. Using the formula P = IV, where I is the current, we find I = P/V = 1200 W / 120 V = 10 A. The time (t) is 5 minutes, which is 300 seconds. The charge (Q) is given by Q = It = 10 A * 300 s = 3000 C.

Question 4

A 6.0 -V storage battery supplies energy to a simple circuit at the constant rate of 48 W. The resistance of the circuit is

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The answer of A 6.0 -V storage battery supplies energy...

Question 5

When two identical resistors are connected in series across a battery, the total power dissipated by them is 20 W. If these resistors are connected in parallel across the same battery, the total power dissipated is

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The answer of When two identical resistors are connected in...

Question 6

The power delivered by the battery in the figure is

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Question 7

You connect two similar heating coils in series on a constant-voltage line. When you later connect them in parallel to the same line, the heat developed per minute, compared with the former rate, is approximately

Accepted Answer

When two identical heating coils are connected in parallel instead of in series, the total resistance of the circuit decreases, leading to an increase in the total current drawn from the power source. Since the power (and thus the heat developed per minute) is proportional to the square of the current (P = I^2R), and the current in the parallel connection is higher for each coil, the total power consumed (and thus heat developed) by the two coils in parallel is four times greater than when they are connected in series.

Question 8

A 12-V car battery may supply 60 A for 2.5 s in order for the starter motor to start the engine. Calculate how much electrical energy has been used.

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Question 9

A current of 0.50 A passes through a lamp with a resistance of 600 Ω. The power supplied to this lamp is

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Question 10

In your four years at college you dry your hair every day for 5 minutes with a 1200-W hair dryer. If the average price of electrical energy was $0.085 per kilowatt-hour, how much did it cost you during this time? Assume 1 year = 365 days.)

Accepted Answer

Power consumed by the hair dryer = 1200 W
Time taken to dry hair per day = 5 minutes = 0.083 hours
Energy consumed per day = Power x Time taken = 1200 x 0.083 = 99.6 Wh = 0.0996 kWh
Total energy consumed in 4 years = 0.0996 x 365 x 4 = 144.936 kWh
Cost of electrical energy per kWh = $0.085
Total cost = 144.936 x $0.085 = $12.34, which is closest to option C, $12.40.

Question 11

A comparison of the power losses P₁, P₂, or P₃) in the resistors of the circuit in the diagram shows that, if R₁ = R₂ = R₃,

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The answer of  A comparison of the power losses...

Question 12

Four identical lightbulbs are connected to a power supply as shown. Which lightbulb consumes the most power?

Accepted Answer

All the bulbs are identical and connected in parallel to the power supply, and therefore, they consume the same amount of power.

Question 13

Four identical lightbulbs are connected to a power supply as shown. Which lightbulb consumes the most power?

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Question 14

Each of three identical electric heaters is rated at 1000 W when operated individually across 100-V lines. When the three are connected in series across a 120-V line, at what rate is electric energy converted to heat energy? Neglect variation of resistance with temperature.)

Accepted Answer

When connected in series, the total resistance is three times the resistance of one heater. The power is calculated using P = V^2/R. With 120 V across three heaters, the power is 0.48 kW.

Question 15

The power delivered by the battery in the circuit shown is

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The answer of  The power delivered by the battery...

Question 16

In this circuit, two batteries, one with a potential difference of 10 V and the other with a potential difference of 20 V, are connected in series across a resistance of 90 Ω. The power delivered by the 10-V battery is approximately

Accepted Answer

To find the power delivered by the 10-V battery, we need to first find the current flowing through the circuit. Using Ohm's Law, we can calculate the current as:

I = V/R = (10 V + 20 V)/90 Ω = 0.333 A

Now, the power delivered by the 10-V battery can be calculated as:

P = VI = (10 V)(0.333 A) = 3.33 W

However, this is an approximation since we have assumed that the internal resistances of the batteries are negligible. In reality, the batteries will have some internal resistance which would cause a voltage drop across them, leading to a slightly lower power output.

Therefore, the closest answer choice to 3.33 W is D) 3.3 W.

Question 17

A variable resistance is connected across the terminals of an ideal storage battery. The curve that might represent the power dissipated in the resistance as a function of the magnitude of the resistance is

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Question 18

In the circuit shown, the power dissipated in the 18-Ω resistor is

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Question 19

A resistor develops heat at the rate of 20 W when the potential difference across its ends is 30 V. The resistance of the resistor is approximately

Accepted Answer

Explanation:Power (P) = 20 WPotential difference (V) = 30 VResistance (R) = V^2/P = (30 V)^2/20 W = 45 Ω

Question 20

A resistor carries a current I. The power dissipated in the resistor is P. What is the power dissipated if the same resistor carries current 3I? Ignore any heating effects.

Accepted Answer

The power dissipated in a resistor is given by P=I^2R, where R is the resistance. If the same resistor carries current 3I, then the power dissipated is P'=(3I)^2R=9I^2R=9P. Therefore, the power dissipated is 9 times the original power when the current is tripled. So, the answer is D.

Quiz 18: Electric Charges in Motion

You leave your 120-W lightbulb on in your room by mistake while you are at school for 8.5 hours. If the price of electrical energy is $0.085 per kilowatt-hour, how much did it cost you?

The curve that best represents the power loss in a resistor is

If it takes you 5 minutes to dry your hair using a 1200-W hair dryer plugged into a 120-V power outlet, how many coulombs of charge pass through your hair dryer?

A 6.0 -V storage battery supplies energy to a simple circuit at the constant rate of 48 W. The resistance of the circuit is

When two identical resistors are connected in series across a battery, the total power dissipated by them is 20 W. If these resistors are connected in parallel across the same battery, the total power dissipated is

The power delivered by the battery in the figure is

You connect two similar heating coils in series on a constant-voltage line. When you later connect them in parallel to the same line, the heat developed per minute, compared with the former rate, is approximately

A 12-V car battery may supply 60 A for 2.5 s in order for the starter motor to start the engine. Calculate how much electrical energy has been used.

A current of 0.50 A passes through a lamp with a resistance of 600 Ω. The power supplied to this lamp is

In your four years at college you dry your hair every day for 5 minutes with a 1200-W hair dryer. If the average price of electrical energy was $0.085 per kilowatt-hour, how much did it cost you during this time? Assume 1 year = 365 days.)

A comparison of the power losses P1, P2, or P3) in the resistors of the circuit in the diagram shows that, if R1 = R2 = R3,

Four identical lightbulbs are connected to a power supply as shown. Which lightbulb consumes the most power?

Four identical lightbulbs are connected to a power supply as shown. Which lightbulb consumes the most power?

Each of three identical electric heaters is rated at 1000 W when operated individually across 100-V lines. When the three are connected in series across a 120-V line, at what rate is electric energy converted to heat energy? Neglect variation of resistance with temperature.)

The power delivered by the battery in the circuit shown is

In this circuit, two batteries, one with a potential difference of 10 V and the other with a potential difference of 20 V, are connected in series across a resistance of 90 Ω. The power delivered by the 10-V battery is approximately

A variable resistance is connected across the terminals of an ideal storage battery. The curve that might represent the power dissipated in the resistance as a function of the magnitude of the resistance is

In the circuit shown, the power dissipated in the 18-Ω resistor is

A resistor develops heat at the rate of 20 W when the potential difference across its ends is 30 V. The resistance of the resistor is approximately

A resistor carries a current I. The power dissipated in the resistor is P. What is the power dissipated if the same resistor carries current 3I? Ignore any heating effects.

A comparison of the power losses P₁, P₂, or P₃) in the resistors of the circuit in the diagram shows that, if R₁ = R₂ = R₃,