1 Conductor in Magnetic Field, Varying Current
A current carrying conductor is in a uniform magnetic field and experiences a force of magnitude F. If I double the current while leaving everything else constant, what is the resulting force needed to hold the wire steady?
- F
- 2F
- 1/2F
- Can’t determine
2 Conductor in Magnetic Field, Varying Field
A current carrying conductor is in a uniform magnetic field and experiences a force of magnitude F. If I double the magnetic field while leaving everything else constant, what is the resulting force?
- F
- 2F
- 1/2F
- Can’t determine
3 Conductor in Magnetic Field, Varying Velocity
I have a wire traveling at a velocity v in a uniform magnetic field. If I double the velocity, what happens?
- EMF doubles
- EMF cuts in half
- EMF stays the same
- Can’t determine
4 Motor, varying current
I have a motor connected to an ideal voltage source. If I double the current supplied to the motor the heat in the motor
- doubles
- quadruples
- halves
- quarters
5 Motor, varying voltage
I have a motor connected to an ideal voltage source. It is running without a load at a certain RPM. If I double the the voltage to the motor the RPM of the motor
- Doubles
- Quadruples
- Halves
- Can’t determine
6 Motor, varying torque
I have a motor connected to an ideal voltage source, if I double the load or torque on the motor the current
- Doubles
- Quadruples
- Halves
- Can’t determine
7 Motor Constant RPM/rps
You have a motor with a 8.5 rpm/V motor constant. What is this in units of radians per second per volt?
8 Motor Constant RPM/NmpA
You have a motor with an 8.5 rpm/V motor constant. What is this in Newton-meters per ampere?
9 Lifting
You have a motor that is running an elevator. The load in units of torque on the elevator is 500 Nm. The motor has a torque constant of 10 Nm per amp and a voltage constant of 1 rpm per volt and a winding resistance of 1 ohm.
- Draw a circuit with the equivalent circuit for the motor.
- What RPM does the motor run at if you apply 100 volts?
10 No load speed
You have a motor with an 8.5 rpm/V motor constant. You connect it to a 48 volt battery.
- What is the no-load rpm?
11 Motor Spinning
You have a motor with a voltage constant of 10 rpm per volt and an internal resistance of 0.1 ohms. You apply 50 volts to the motor and it spins at 400 rpm while loaded.
- Draw a circuit with the equivalent circuit for the motor.
- What is the current flowing through the motor?
12 Motor Efficiency
Using our equivalent circuit model, explain why the electrical power we give to a motor is greater than the mechanical output power.
(Since current is proportional to torque and the generated voltage is proportional to speed, wouldn’t we expect them to be equal?)
13 Generated Voltage and Terminal Voltage
Under what conditions is the voltage generated by the motor the same as the voltage that appears at the motor terminals?
14 Fan Motor Voltage
A fan is spinning at 1000 RPM. The motor has a Kv of 10 RPM per volt and an internal resistance of 0.1 ohms. The motor is consuming 50 amps of current. What is the voltage being supplied to the motor?
RQ 1
Read Chapter 24 and 25 on magnetism and magnetic induction in Hewitt Conceptual Physics and answer the following questions:
- Under what conditions does a wire in a magnetic field experience a force?
- What does the force depend on?
RQ 2 Hughes and Drury Chapter 1 Electric motors - The Basics
Read Hughes and Drury 5th Edition , Chapter 1. Focus on sections 1.1–1.2 and 1.6–1.8.
- How is the equivalent circuit model similar to a battery and how is it different?
- What does the voltage of the ideal voltage source in the equivalent circuit model depend on?
RQ 3 Hughes and Drury Chapter 3 DC Motors
Read Hughes and Drury 5th Edition , Chapter 3. Focus on sections 3.3 and 3.4.
- How are the torque constant k_t and the e.m.f. constant k_e related?
- What is meant by the no-load speed?
RQ 4 Energy Efficiency Reading
Read the Department of Energy Motor Handbook Chapters 1 and 2.
- What is the EISA?
- Why are minimum efficiency standards important?