Electrical Resistance - Questions

Electrical Resistance
































The following notes are attached to some electrical devices. Which one can you safely ignore?

(A) Danger! One million volts!
(B) Danger! One million amps!
(C) Danger! One million ohms!

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The following notes are attached to some electrical devices. Which one can you safely ignore?

(A) Danger! One million volts! --- No.
That could force a large current through you.

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The following notes are attached to some electrical devices. Which one can you safely ignore?

(B) Danger! One million amps! --- No.
That much current would not be healthy if it went through you.

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The following notes are attached to some electrical devices. Which one can you safely ignore?

(C) Danger! One million ohms! --- Yes
Go ahead and ignore it. It's just a good insulator.

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A voltage drop of 3V causes 5A of current to flow through a light bulb. Assume (incorrectly) that the bulb obeys Ohm's law. What voltage drop would cause a current of 15A to flow through the bulb?

(A) 5V. (B) 9V. (C)25V. (D)27V.


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A voltage drop of 3V causes 5A of current to flow through a light bulb. Assume (incorrectly) that the bulb obeys Ohm's law. What voltage drop would cause a current of 15A to flow through the bulb?
(A) 5V. --- No.
Calculate the factor that the current is multiplied by.

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A voltage drop of 3V causes 5A of current to flow through a light bulb. Assume (incorrectly) that the bulb obeys Ohm's law. What voltage drop would cause a current of 15A to flow through the bulb?
(B) 9V. --- Yes.
Current multiplied by 3 so voltage is multiplied by 3.

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A voltage drop of 3V causes 5A of current to flow through a light bulb. Assume (incorrectly) that the bulb obeys Ohm's law. What voltage drop would cause a current of 15A to flow through the bulb?
(C) 25V. --- No.
First divide new current by old current: 15A/5A = 3.

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A voltage drop of 3V causes 5A of current to flow through a light bulb. Assume (incorrectly) that the bulb obeys Ohm's law. What voltage drop would cause a current of 15A to flow through the bulb?
(D) 27V. --- No.
Voltage is proportional to current not to current squared.

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Most devices violate Ohm's Law somewhat. Which of the following electrical devices violates Ohm's Law the most?

(A) Two feet of copper wire.
(B) An insulator.
(C) A diode.
(D) A 4700 ohm resistor.

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Most devices violate Ohm's Law somewhat. Which of the following electrical devices violates Ohm's Law the most?

(A) Two feet of copper wire. --- No.

It's resistance would be small but constant.

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Most devices violate Ohm's Law somewhat. Which of the following electrical devices violates Ohm's Law the most?

(B) An insulator. --- No.
Its resistance would be very large but constant.

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Most devices violate Ohm's Law somewhat. Which of the following electrical devices violates Ohm's Law the most?

(C) A diode. --- Yes.
Resistance high in one direction, low in the other.

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Most devices violate Ohm's Law somewhat. Which of the following electrical devices violates Ohm's Law the most?

(D) A 4700 ohm resistor. --- No.

Constant resistance (namely 4700 ohms).

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Calculate (based on the assumptions made in class) how much of a shock a person with clean hands can get from a 12 volt automobile battery.

(A) Not even a tingle.
(B) A tingle but no pain.
(C) A painful shock.
(D) Death.

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Calculate (based on the assumptions made in class) how much of a shock a person with clean hands can get from a 12 volt automobile battery.

(A) Not even a tingle. --- No.
Assuming 500 ohms gives more than 0.001A.

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Calculate (based on the assumptions made in class) how much of a shock a person with clean hands can get from a 12 volt automobile battery.

(B) A tingle but no pain. --- No.
Assuming 500 ohms gives more than 0.001A

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Calculate (based on the assumptions made in class) how much of a shock a person with clean hands can get from a 12 volt automobile battery.

(C) A painful shock. --- Yes.

I = 12V/500 = 0.024A > 0.01A

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Calculate (based on the assumptions made in class) how much of a shock a person with clean hands can get from a 12 volt automobile battery.

(D) Death. --- No.

Assuming 500 gives less than 0.1A.

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