Question 1

A hair dryer draws 1,050 W,a curling iron draws 900 W,and an electric light fixture draws 450 W.If all three of these appliances are operating in parallel on a 120-V circuit,what is the total current drawn?
A) 6.7 A
B) 20 A
C) 1.9 A
D) 27.5 A
E) ​8.8 A

Accepted Answer

The answer of A hair dryer draws 1,050 W,a curling...

Question 2

Three resistors,each of different value,are used in a circuit with a power source supplying 12 volts.For which of the following resistor combinations is the total power supplied the greatest?
A) all three resistors in series
B) all three resistors in parallel
C) two of the resistors in parallel with the third resistor in series with the parallel pair
D) This cannot be found until it is known which resistor is in series with the parallel pair.

Accepted Answer

According to Ohm's Law, when resistors are connected in parallel, the equivalent resistance decreases, resulting in a larger current flowing through the circuit. This, in turn, leads to a higher total power being dissipated across the resistors compared to when they are connected in series. Therefore, the greatest total power supplied will be when all three resistors are connected in parallel (choice B).

Question 3

A series RC circuit,which is made from a battery,a switch,a resistor,and a 5-μF capacitor,has a time constant of 8 ms.If an additional 7-μF is added in series to the 5-μF capacitor,what is the resulting time constant?
A) 11.2 ms
B) 4.7 ms
C) 0.5 ms
D) ​13.7 ms
E) ​This cannot be found without the value of the resistance being given.

Accepted Answer

The time constant τ = RC. When capacitors are in series, the total capacitance C_total is given by 1/C_total = 1/C1 + 1/C2. For 5-μF and 7-μF in series, C_total = 2.917 μF. The original time constant is 8 ms with 5-μF, so R = τ/C = 8 ms / 5 μF. The new time constant τ' = R * C_total = (8 ms / 5 μF) * 2.917 μF = 4.7 ms.

Question 4

Household circuits are wired in ________.
A) series
B) parallel
C) both series and parallel
D) neither series nor parallel

Accepted Answer

Household circuits are wired in parallel, which means each appliance or device is connected to the circuit separately, allowing them to function independently without affecting each other's operation. This also means that if one appliance fails, it won't affect the operation of others on the same circuit.

Question 5

The following three appliances are connected to a 120-V house circuit: i)toaster,1,250 W,ii)coffee pot,600 W,and iii)microwave,800 W.If all were operated at the same time,what total current would they draw?
A) 2.2 A
B) 44.6 A
C) 7.4 A
D) 22.1 A
E) ​10.4 A

Accepted Answer

The total power is 1,250 W + 600 W + 800 W = 2,650 W. The total current is 2,650 W / 120 V = 22.1 A.

Question 6

A 1 000-V battery,a 3 000-Ω resistor and a 0.50-µF capacitor are connected in series with a switch.The time constant for such a circuit,designated by the Greek letter,τ,is defined as the time required to charge the capacitor to 63% of its capacity after the switch is closed.What is the value of τ for this circuit? A) 6.0 × 10⁹ s B) 1.7 × 10−¹⁰ s C) 1.7 × 10−⁷ s D) 1.5 × 10−³ s

Accepted Answer

The answer of A 1 000-V battery,a 3 000-Ω resistor...

Question 7

In an RC circuit using two capacitors in series with two resistors,which of the following combinations would give the greatest time constant?
A) both capacitors in series placed in series with both resistors in series
B) both capacitors in parallel placed in series with both resistors in parallel
C) both capacitors in series placed in series with both resistors in parallel
D) both capacitors in parallel placed in series with both resistors in series

Accepted Answer

The time constant ($\tau$) of an RC circuit is given by $\tau = RC$, where $R$ is the resistance and $C$ is the capacitance. For capacitors in parallel, the total capacitance ($C_{total}$) is the sum of the individual capacitances ($C_{total} = C_1 + C_2$). For resistors in series, the total resistance ($R_{total}$) is the sum of the individual resistances ($R_{total} = R_1 + R_2$). Therefore, having both capacitors in parallel increases the total capacitance, and having both resistors in series increases the total resistance, which together maximize the time constant ($\tau$).

Question 8

A certain capacitor is charged to 10 V and then,at t = 0,allowed to discharge through a certain resistor.There will be a certain time before the voltage across the capacitor reaches 5 V.This time can be decreased for this circuit by increasing:
A) the size of the capacitor.
B) the size of the resistor.
C) the size of the time constant.
D) None of the above.

Accepted Answer

The answer of A certain capacitor is charged to 10...

Question 9

Using a resistor and two different value capacitors,which of the following combinations in an RC circuit would give the greatest time constant?
A) the resistor in series with both capacitors in series with each other
B) the resistor in series with both capacitors in parallel with each other
C) the resistor in series with the larger value capacitor
D) the resistor in series with the lower value capacitor

Accepted Answer

The answer of Using a resistor and two different value...

Question 10

Kirchhoff's rules are the junction rule and the loop rule.Which of the following statements is true?
A) Both rules are based on the conservation of charge.
B) Both rules are based on the conservation of energy.
C) The junction rule is based on the conservation of charge,and the loop rule is based on the conservation of energy.
D) The junction rule is based on the conservation of energy,and the loop rule is based on the conservation of charge.

Accepted Answer

The junction rule is based on the principle of conservation of charge, which states that the total current flowing into a junction must be equal to the total current flowing out of it. The loop rule is based on the principle of conservation of energy, which states that the total energy supplied to a closed loop must be equal to the total energy returned by it. Therefore, option C is the correct choice.

Question 11

Using a capacitor and two different value resistors,which of the following combinations in an RC circuit would give the greatest time constant?
A) the capacitor in series with both resistors in series with each other
B) the capacitor in series with both resistors in parallel with each other
C) the capacitor in series with the higher value resistor
D) the capacitor in series with the lower value resistor

Accepted Answer

The time constant ($\tau$) of an RC circuit is given by $\tau = RC$, where $R$ is the resistance and $C$ is the capacitance. In option A, the resistors in series combine their resistances, resulting in a higher total resistance compared to the other configurations, thus giving the greatest time constant.

Question 12

A voltage source of 15 V is connected to a series RC circuit where R = 2 × 10⁶ Ω,and C = 1 µF.Find the amount of time required for the current in the circuit to decay to 6% of its original value.Hint: This is the same amount of time for the capacitor to reach 94% of its maximum charge. A) 1.6 s B) 3.6 s C) 0.5 s D) 5.6 s E) 11.2 s

Accepted Answer

The answer of A voltage source of 15 V is...

Question 13

In applications where electrical shocks may be more likely,such as around water in kitchens and bathrooms,special outlets called GFI's are used.What does GFI stand for?
A) get free instantly
B) ground-fault interrupter
C) give fast interruption
D) gravity-free insulator

Accepted Answer

GFI stands for ground-fault interrupter, which is a special outlet that protects against electric shock by quickly interrupting the flow of electricity if it detects any change in current flow.

Question 14

A 1 000-V battery,a 3 000-Ω resistor,and a 0.50-μF capacitor are connected in series with a switch.The time constant for such a circuit,designated by the Greek letter,τ,is defined as the time that the capacitor takes to charge to 63% of its capacity after the switch is closed.What is the current in the circuit at a time interval of τ seconds after the switch has been closed? 
A) 0.14 A
B) 0.21 A
C) 0.12 A
D) 0.32 A

Accepted Answer

The answer of A 1 000-V battery,a 3 000-Ω resistor,and...

Question 15

A series RC circuit has a time constant of 1.0 s.The battery has a voltage of 50 V and the maximum current just after closing the switch is 500 mA.The capacitor is initially uncharged.What is the charge on the capacitor 2.0 s after the switch is closed? 
A) 0.43 C
B) 0 66 C
C) 0.86 C
D) 0.99 C

Accepted Answer

The answer of A series RC circuit has a time...

Question 16

What is the maximum number of 50-W light bulbs you can connect in parallel in a 100-V home circuit without tripping the 40-A circuit breaker?
A) 20
B) 39
C) 79
D) 59
E) ​58

Accepted Answer

The total current drawn by the bulbs should not exceed 40 A. Each 50-W bulb at 100 V draws 0.5 A (Power = Voltage x Current, so Current = Power/Voltage = 50W/100V = 0.5A). Therefore, the maximum number of bulbs is 40 A / 0.5 A per bulb = 80 bulbs. However, to avoid tripping the breaker, you should use one less, which is 79 bulbs.

Question 17

Household 120-V outlets are made to accept three-pronged plugs.One of the prongs attaches to the "live" wire at 120 V,and another attaches to the "neutral" wire that is connected to ground.What is the round third prong for?
A) It serves as a backup to the hot wire.
B) It lets the appliance run if the neutral wire breaks.
C) It connects the case of the appliance directly to ground for safety purposes.
D) Nothing electrical,it is for mechanical sturdiness.

Accepted Answer

The round third prong is called the ground pin or earth pin, and it is designed to provide an additional safety measure to protect against electric shock. It connects the metal case of the appliance directly to the ground, which provides a safe path for any electrical current that might accidentally come into contact with the case. This can prevent serious injury or even death in some cases.

Quiz 18: Direct-Current Circuits Sources of EMF

A hair dryer draws 1,050 W,a curling iron draws 900 W,and an electric light fixture draws 450 W.If all three of these appliances are operating in parallel on a 120-V circuit,what is the total current drawn?

Three resistors,each of different value,are used in a circuit with a power source supplying 12 volts.For which of the following resistor combinations is the total power supplied the greatest?

A series RC circuit,which is made from a battery,a switch,a resistor,and a 5-μF capacitor,has a time constant of 8 ms.If an additional 7-μF is added in series to the 5-μF capacitor,what is the resulting time constant?

Household circuits are wired in ________.

The following three appliances are connected to a 120-V house circuit: i) toaster,1,250 W,ii) coffee pot,600 W,and iii) microwave,800 W.If all were operated at the same time,what total current would they draw?

In an RC circuit using two capacitors in series with two resistors,which of the following combinations would give the greatest time constant?

A certain capacitor is charged to 10 V and then,at t = 0,allowed to discharge through a certain resistor.There will be a certain time before the voltage across the capacitor reaches 5 V.This time can be decreased for this circuit by increasing:

Using a resistor and two different value capacitors,which of the following combinations in an RC circuit would give the greatest time constant?

Kirchhoff's rules are the junction rule and the loop rule.Which of the following statements is true?

Using a capacitor and two different value resistors,which of the following combinations in an RC circuit would give the greatest time constant?

A voltage source of 15 V is connected to a series RC circuit where R = 2 × 10⁶ Ω,and C = 1 µF.Find the amount of time required for the current in the circuit to decay to 6% of its original value.Hint: This is the same amount of time for the capacitor to reach 94% of its maximum charge.

In applications where electrical shocks may be more likely,such as around water in kitchens and bathrooms,special outlets called GFI's are used.What does GFI stand for?

A series RC circuit has a time constant of 1.0 s.The battery has a voltage of 50 V and the maximum current just after closing the switch is 500 mA.The capacitor is initially uncharged.What is the charge on the capacitor 2.0 s after the switch is closed?

What is the maximum number of 50-W light bulbs you can connect in parallel in a 100-V home circuit without tripping the 40-A circuit breaker?

Household 120-V outlets are made to accept three-pronged plugs.One of the prongs attaches to the "live" wire at 120 V,and another attaches to the "neutral" wire that is connected to ground.What is the round third prong for?