Jackson

Question 1

What factors cause torque to vary?

Answer 1

Using the formula τ = nBIAcosθ and τ = Fd,

we can infer that for torque to increase: -

• the number of turns of the coil must increase
• the strength of the magnetic field must increase
• the current in the wire must increase
• the area of the wire must increase
• the angle between the coil and the plane of the wire must be as close to perpendicular as possible OR -
• the distance the coil is from the pivot must increase

Question 2

Explain why more winds of the coil produce a large force on the wire

Answer 2

Each wind of the coil experiences a force individually, the more winds of the coil, the more force the coil experiences as a system.

Question 3

A lever is free to rotate around a point P.

Calculate the magnitude of the torque acting on the lever if a 32N force acts at right angles to the lever at a distance of 0.6m

Answer 3

τ = Fd. τ = 32 x 0.6 = 19.2 Nm

Question 4

A door with a pivot P experiences a force of 30N at 60° to the horizontal. At a distance of 1.2m. Calculate the torque

Answer 4

τ = Fdsinθ

τ = 30 x 1.2 x sin60

τ = 18Nm

Question 5

A coil contains 15 loops and it’s plane is sitting at an angle of 30° to the direction of a magnetic field of 6.7mT. The coil has dimensions 16cm x 10cm and has a 14 mA current passing through it. Determine the torque

Answer 5

τ = nBIAcosθ

τ = 15 x (6.7x10^-3) x (14x10^-3) x (16x10^-3 x 10x10^-3) x cos30

= 194.960 nNm

Question 6

Define torque and give an example of where it appears

Answer 6

Torque is a turning force (a moment) measured in Nm. It is the tendency of an object to rotate around a point.

Just as a force is a push or pull, torque can be thought of as a rotation or twist. Torque often appears in motors when the coil rotates around a central point.