Torque

Definition

Torque is a measure of the rotational force that causes an object to rotate about an axis, fulcrum, or pivot. It is the product of the force applied and the distance between the line of action of the force and the axis of rotation.

5 Must Know Facts For Your Next Test

1. Torque is responsible for the rotational motion of objects, such as the rotation of a door around its hinges or the spinning of a bicycle wheel.
2. The magnitude of the torque is directly proportional to the force applied and the lever arm, and it is inversely proportional to the distance from the axis of rotation.
3. In the context of electric dipoles (5.7), torque plays a role in the alignment of the dipole moment with an external electric field.
4. In the context of electric generators and back EMF (13.6), torque is responsible for the generation of the back EMF, which opposes the rotation of the generator's rotor.
5. Torque is a vector quantity, meaning it has both magnitude and direction, and it is often represented by the Greek letter tau (τ).

Review Questions

• Explain how the concept of torque applies to the behavior of electric dipoles in an external electric field.
  • When an electric dipole is placed in an external electric field, a torque is exerted on the dipole. This torque causes the dipole to align itself with the direction of the electric field. The magnitude of the torque is proportional to the strength of the electric field, the magnitude of the dipole moment, and the sine of the angle between the dipole moment and the electric field. This torque acts to minimize the potential energy of the dipole in the electric field, leading to the alignment of the dipole with the field.
• Describe the role of torque in the operation of an electric generator and the generation of back EMF.
  • In an electric generator, the rotation of the rotor is driven by the application of a torque, typically from a prime mover such as a turbine or engine. This torque causes the rotor to spin, which in turn induces an electromotive force (EMF) in the generator's windings. The induced EMF opposes the rotation of the rotor, creating a back EMF that acts as a counter-torque. This back EMF is directly proportional to the angular velocity of the rotor and the strength of the magnetic field in the generator. The balance between the applied torque and the back EMF torque determines the generator's output voltage and power.
• Analyze how the concept of torque can be used to understand the relationship between the input torque and the output voltage in an electric generator, and how this relationship is influenced by the generator's design and operating conditions.
  • The relationship between the input torque and the output voltage in an electric generator can be understood through the concept of torque. The input torque, applied by a prime mover, causes the generator's rotor to spin, which in turn induces an EMF in the windings. This induced EMF creates a back EMF that acts as a counter-torque, opposing the rotation of the rotor. The balance between the input torque and the back EMF torque determines the generator's output voltage and power. The generator's design, such as the number of poles, the strength of the magnetic field, and the winding configuration, as well as the operating conditions, such as the rotational speed and load, all influence this relationship. By analyzing the torque balance, one can understand how changes in the generator's design or operating conditions affect the output voltage and power generation.

Related terms

Moment: The moment is the tendency of a force to cause rotational motion about a specific point or axis. Torque is a type of moment.

Lever Arm: The lever arm is the perpendicular distance from the axis of rotation to the line of action of the applied force, which determines the magnitude of the torque.

Angular Acceleration: Angular acceleration is the rate of change of angular velocity, and it is caused by the application of torque to an object.