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B.Tech EEE Electric Current, Resistance, and Ohm's Law — practice questions — page 3

Explore 90 free Electric Current, Resistance, and Ohm's Law questions in B.Tech EEE Electrical Engineering. Open each question or exercise to read its content, reference answers and available explanation.

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Electric Current, Resistance, and Ohm's Law questions and exercises with answers

Showing questions 61–90 of 90.

The same 100 MW is sent down the same 1.00 ohm line at 25 kV instead of 200 kV. What fraction of the power is now lost?Read the answer and worked solution →Why is AC rather than DC used in most large-scale power distribution systems?Read the answer and worked solution →Who set up a DC power-distribution system in New York City in the late 1800s, believing AC shocks to be more harmful?Read the answer and worked solution →What reasons are given for AC winning out over DC for distribution?Read the answer and worked solution →Electricity presents which two hazards?Read the answer and worked solution →A thermal hazard is defined by which situation?Read the answer and worked solution →A short circuit is which of these?Read the answer and worked solution →A short of resistance 0.100 ohm forms across a 120-V supply. What thermal power does it dissipate?Read the answer and worked solution →A worn appliance cord has a resistance of 2.00 ohm instead of the 0.100 ohm it should have. What power is dissipated in it when 10.0 A flows?Read the answer and worked solution →What do fuses and circuit breakers do in a circuit?Read the answer and worked solution →Why is it easier for a large circuit breaker to interrupt AC than DC?Read the answer and worked solution →Which set of factors determines the effect an electrical shock has on a person?Read the answer and worked solution →Above what current can a shock cause sustained muscular contraction, so that the victim cannot let go?Read the answer and worked solution →Over what current range does ventricular fibrillation become possible?Read the answer and worked solution →At which frequencies is the human body most sensitive to electrical current?Read the answer and worked solution →What happens to electrical current in a person at very high frequency?Read the answer and worked solution →Nerve conduction is the general term for which process?Read the answer and worked solution →In its resting state, which ions can cross the membrane of a neuron?Read the answer and worked solution →Membrane voltages exist across almost all animal cells. In which cells are they largest?Read the answer and worked solution →Depolarization of a neuron membrane is driven by which ion movement?Read the answer and worked solution →What returns a neuron to its resting potential after it has depolarized?Read the answer and worked solution →About how fast does a nerve impulse travel along a cell membrane?Read the answer and worked solution →Compared with an unmyelinated one, how does a myelinated axon carry a nerve impulse?Read the answer and worked solution →What name is given to the unmyelinated gaps that separate the myelin sheaths along an axon?Read the answer and worked solution →Myelin is an insulator. What does that insulation achieve for an axon?Read the answer and worked solution →Why is no cell energy spent in the myelinated stretches of an axon?Read the answer and worked solution →Multiple sclerosis arises through which mechanism?Read the answer and worked solution →In a three-electrode electrocardiogram, the lead II potential is measured between which two points?Read the answer and worked solution →The QRS complex of an electrocardiogram is generated by which event?Read the answer and worked solution →The T wave of an electrocardiogram is generated by which event?Read the answer and worked solution →

Worked practice questions

The same 100 MW is sent down the same 1.00 ohm line at 25 kV instead of 200 kV. What fraction of the power is now lost?

  1. 0.250 percent
  2. 1.60 percent
  3. 16.0 percent
  4. 32.0 percent
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Correct answer: C. 16.0 percent

1. First find the current: I = P / V = (100 x 10^6 W) / (25 x 10^3 V) = 4000 A. 2. Then the line loss: P_loss = I squared R = (4000 A) squared (1.00 ohm) = 16.0 x 10^6 W. 3. That is 16.0 MW lost out of the 100 MW sent. 4. As a percentage, (16.0 MW / 100 MW) x 100 = 16.0 percent. 5. Dropping the voltage by a factor of eight raised the current by eight and the loss by sixty four. 6. 0.250 percent is the loss at 200 kV, so choosing it ignores the change of voltage entirely. 7. 1.60 percent scales the loss linearly with voltage instead of with its square. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section Why Use AC for Power Distribution?_

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Why is AC rather than DC used in most large-scale power distribution systems?

  1. AC currents are smaller at equal power
  2. AC lines have lower resistance than DC
  3. AC voltages are easier to raise and lower
  4. AC generators cost less than DC ones
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Correct answer: C. AC voltages are easier to raise and lower

1. Long-distance transmission is cheap only if the voltage is very high, because the current is then small. 2. But the voltage delivered to a user has to be brought back down for safety. 3. So the system needs voltage to be changed twice, up at the plant and down at the point of use. 4. Changing an AC voltage is far easier than changing a DC one, which decides the choice. 5. A line's resistance is a property of its metal and geometry, so it does not depend on whether the current alternates. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section Why Use AC for Power Distribution?_

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Who set up a DC power-distribution system in New York City in the late 1800s, believing AC shocks to be more harmful?

  1. Nikola Tesla
  2. Westinghouse
  3. Georg Simon Ohm
  4. Thomas Edison
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Correct answer: D. Thomas Edison

1. The choice between AC and DC distribution was fought out commercially in the late 1800s. 2. Thomas Edison held that AC shocks were the more harmful and built a DC system in New York City. 3. George Westinghouse and Nikola Tesla argued for AC on the other side of that dispute. 4. AC won in the end, so Tesla and Westinghouse are the advocates rather than the DC builder asked for. 5. Ohm died decades before any distribution system existed, so he cannot be the answer. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section Why Use AC for Power Distribution?_

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