Electric Power - Questions

Electric Power
































Which of the following is a unit of electrical power?

(A) joule.
(B) ampere.
(C) watt.
(D) volt.
(E) coulomb.

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Which of the following is a unit of electrical power?

(A) joule. --- No.

That is a unit of energy. Power is energy per unit time.

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Which of the following is a unit of electrical power?

(B) ampere. --- No.

That is a unit of current --- charge per unit tiime.

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Which of the following is a unit of electrical power?

(C) watt. --- Yes.

1 watt = 1 joule per unit time, same as mechanical power.

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Which of the following is a unit of electrical power?

(D) volt. --- No.

That is the unit of potential --- energy per unit charge. Power is energy per unit time.

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Which of the following is a unit of electrical power?

(E) coulomb. --- No.

That is the unit of electric charge. Power is energy per unit time.

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Suppose that your 12 volt battery must supply a kilowatt of electrical power to operate the starter in your car. Approximately how much current must it supply?

(A) 12A. (B) 80A. (C) 12,000A. (D) 1000A.

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Suppose that your 12 volt battery must supply a kilowatt of electrical power to operate the starter in your car. Approximately how much current must it supply?

(A) 12A. --- No. Use P = IV

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Suppose that your 12 volt battery must supply a kilowatt of electrical power to operate the starter in your car. Approximately how much current must it supply?

(B) 80A. -- Yes, IV = (80A)(12V) = 960W
---- approximately 1000W.

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Suppose that your 12 volt battery must supply a kilowatt of electrical power to operate the starter in your car. Approximately how much current must it supply?

(C) 12,000A. --- No.
Multiply voltage by current, not by power.

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Suppose that your 12 volt battery must supply a kilowatt of electrical power to operate the starter in your car. Approximately how much current must it supply?

(D) 1000A. --- No. Use P = IV

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A light bulb passes 3A of current while a voltage drop of 6V appears across its terminals. At what rate is the bulb using electrical power?

(A) 2W, (B) 3W. (C) 6W. (D) 18W,


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A light bulb passes 3A of current while a voltage drop of 6V appears across its terminals. At what rate is the bulb using electrical power?

(A) 2W, --- No.
Multiply current times voltage.

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A light bulb passes 3A of current while a voltage drop of 6V appears across its terminals. At what rate is the bulb using electrical power?

(B) 3W. --- No.
Use the formula P = IV.

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A light bulb passes 3A of current while a voltage drop of 6V appears across its terminals. At what rate is the bulb using electrical power?

(C) 6W. --- No.
Use the formula P = IV.

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A light bulb passes 3A of current while a voltage drop of 6V appears across its terminals. At what rate is the bulb using electrical power?

(D) 18W, --- Yes
P = IV = (3A)(6V) = 18W

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An air conditioner uses 10A of 120V household electric current. If electric power costs $0.1 per killowatt-hour, what does it cost to run this air conditioner for one hour?

(A) $0.012, (B) $0.100,
(C) $0.120, (D) $10.00

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An air conditioner uses 10A of 120V household electric current. If electric power costs $0.1 per killowatt-hour, what does it cost to run this air conditioner for one hour?
(A) $0.012, --- No.
Use P=IV, 1kW = 1000W

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An air conditioner uses 10A of 120V household electric current. If electric power costs $0.1 per killowatt-hour, what does it cost to run this air conditioner for one hour?
(B) $0.100, --- No.
Calculate the power from P=IV

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An air conditioner uses 10A of 120V household electric current. If electric power costs $0.1 per killowatt-hour, what does it cost to run this air conditioner for one hour?
(C) $0.120, --- Yes, about 12 cents.
P = IV = (10A)(120V) = 1200W = 1.2kW.
1.2kWhr = (1.2)($0.1) = $0.12

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An air conditioner uses 10A of 120V household electric current. If electric power costs $0.1 per killowatt-hour, what does it cost to run this air conditioner for one hour?
(D) $10.00 --- No.
Use P = IV to calculate the answer.

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