Current Loop's Torque and Force [Part I]

Motor

A device that uses magnetic force on current-carrying wires to convert electrical energy into mechanical work

Torque

The twisting force that makes an object rotate around an axis

Motor Principle

Loops of wire in a magnetic field experience torque when current flows, causing a shaft to rotate.

Through the rotation of the motor’s shaft.

Electrical energy inside the motor is converted into the Mechanical work through what?

Torque stops when the loops’s surface area is aligned with the magnetic field.

When does the torque stop inside a motor?

The current in the loop must be reversed using commutators and brushes

What should be done to ensure the continual torque and continuous rotation in a motor?

Role of commutators and brushes

Commutators and brushes reverse the direction of current in the loop at the right moment, maintaining continual torque in the motor.

current flow, continual motion

The commutator is set to reverse the ___________ at set points to keep _______________ in the motor.

Three

Number of contact areas a basic commutator has.

To avoid dead spots where the loop would have zero instantaneous torque.

Why does a basic commutator have three contact areas?

Dead spot in a motor

A position where the loop would produce zero instantaneous torque.

Brushes press against the commutator, creating electrical contact during the spinning motion.

What is the purpose of having brushes in a motor?

DC electric motor (with no net torque)

DC electric motor (with net torque)

magnetic field

The rectangular wire loop in a motor is placed in a ______________

RHR-1

According to the _____ the forces on the sides of the loop are opposite in direction

The loop experiences a net torque and rotates

What happens to the loop when opposite forces act on its sides.

No current flows through the loop

What happens to the current when the brushes touch both commutator segments?

No torque acts on the loop

What happens when no current flows through the loop?

It continues due to the initial velocity from the earlier torque.

Why does the loop keep spinning even when no current flows?

Current flows again, but in the opposite direction.

What happens when the loop flips over?

Because the current reverses each half-turn, recreating torque in the same rotational direction.

Why does the loop keep rotating continually?

forces, torques

In a uniform magnetic field, a current-carrying loop of wire such as a loop in motor, experiences both ______ and _______ on the loop.

B = B ĵ

Formula for the loop in a uniform magnetic field

Il × B

Magnetic force on a straight current-carrying wire of length l

ΣFnet = F1 + F2 + F3 + F4 = 0

Equation for the net force on the loop

F1 = (I*a*B*sin(90° - θ))î = (I*a*B*cos(θ))î

Equation for the force on side 1 of the rectangular loop

Side 3

The side of the loop where the current flows in the opposite direction of that of side 1

F3 = -(I*a*B*sin(90° + θ))î = -(I*a*B*cos(θ))î

Equation for the force on side 3 of the rectangular loop

Side 2 and Side 4

The sides of the loop where the currents are perpendicular to the magnetic field

F2 = I*b*B*k̂

Equation for the force on side 2 of the rectangular loop

F4 = -I*b*B*k̂

Equation for the force on side 4 of the rectangular loop

Yes, it is true

Is it true that there is no net force on a current loop in a uniform magnetic field?

A rectangular current loop in a uniform magnetic field which is being subjected to a net torque but not a net force.

n̂

(i)

θ

(ii)

B

(iii)

F3

(iv)

F2

(v)

F1

(vi)

I

(vii)

F4

(viii)

Side view

B

(1)

θ

(2)

n̂

(3)

x

(4)

(a - x)

(5)

F2

(6)

F4

(7)