Even if the rotor of a simple DC motor has negligible resistance, there is still a non-vanishing potential difference across its terminals when the motor is in used and current is running through it. Why is this so? (A) A motor converts electrical energy to mechanical energy so the power input P = IV, where V is the potential difference, cannot be zero. There should then be a non-vanishing V to push the charges in the rotor, for the motor to perform a meaningful amount of work. (B) The potential difference across the terminals of a motor is simply the applied voltage from a suitable source, presumably with non-zero value. (C) Positive and negative charges in a rotor are affected in different ways when it rotates upon application of electricity. Whereas negative charges cannot move, the positive charges can, causing a potential difference due to their net separation. (D) When the rotor rotates, resistance develops due to the brush system reversing the current direction in the rotor. This then leads to a potential difference by virtue of the relation V = IR, where R is the resistance, I is current, and V is the voltage. (E) Different sides of the rotor move at different velocities. This differ- ence implies different kinetic energies which then translates to a need for energy input. The energy input corresponds to a non-vanishing applied potential difference.
Even if the rotor of a simple DC motor has negligible resistance, there is still a non-vanishing potential difference across its terminals when the motor is in used and current is running through it. Why is this so? (A) A motor converts electrical energy to mechanical energy so the power input P = IV, where V is the potential difference, cannot be zero. There should then be a non-vanishing V to push the charges in the rotor, for the motor to perform a meaningful amount of work. (B) The potential difference across the terminals of a motor is simply the applied voltage from a suitable source, presumably with non-zero value. (C) Positive and negative charges in a rotor are affected in different ways when it rotates upon application of electricity. Whereas negative charges cannot move, the positive charges can, causing a potential difference due to their net separation. (D) When the rotor rotates, resistance develops due to the brush system reversing the current direction in the rotor. This then leads to a potential difference by virtue of the relation V = IR, where R is the resistance, I is current, and V is the voltage. (E) Different sides of the rotor move at different velocities. This differ- ence implies different kinetic energies which then translates to a need for energy input. The energy input corresponds to a non-vanishing applied potential difference.
Glencoe Physics: Principles and Problems, Student Edition
1st Edition
ISBN:9780078807213
Author:Paul W. Zitzewitz
Publisher:Paul W. Zitzewitz
Chapter25: Electromagnetic Induction
Section: Chapter Questions
Problem 69A
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Transcribed Image Text:Even if the rotor of a simple DC motor has negligible resistance,
there is still a non-vanishing potential difference across its terminals when
the motor is in used and current is running through it. Why is this so?
(A) A motor converts electrical energy to mechanical energy so the power
input P = IV, where V is the potential difference, cannot be zero.
There should then be a non-vanishing V to push the charges in the
rotor, for the motor to perform a meaningful amount of work.
(B) The potential difference across the terminals of a motor is simply
SS
the applied voltage from a suitable source, presumably with non-zer
value.
(C) Positive and negative charges in a rotor are affected in different ways
when it rotates upon application of electricity. Whereas negative
charges cannot move, the positive charges can, causing a potential
difference due to their net separation.
(D) When the rotor rotates, resistance develops due to the brush system
reversing the current direction in the rotor. This then leads to a
potential difference by virtue of the relation V = IR, where R is the
resistance, I is current, and V is the voltage.
(E) Different sides of the rotor move at different velocities. This differ-
ence implies different kinetic energies which then translates to a need
for energy input. The energy input corresponds to a non-vanishing
applied potential difference.
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