The motor effect

விளையாடிக் கற்றுக்கொள்ளுங்கள்

ஆற்றல் சம்பாதிக்க இந்த கேள்விகளுக்குப் பதிலளியுங்கள், பின்னர் மீன் பிடித்து ஆராயுங்கள். கணக்கு தேவையில்லை.

கல்வியாளர்களுக்கு: The motor effect (Science, Physics)-க்கான தயாரான பாட ஸ்லைடுகள், திருப்புதல் குறிப்புகள் — உங்கள் பாடத்தில் அவற்றைப் பயன்படுத்தவும், அல்லது கற்பவர்கள் நேரலை விளையாட்டாக விளையாடும் ஊடாடும் வகுப்பு செயல்பாடாக தலைப்பை இயக்கவும்.

பாட குறிப்புகள்

Magnetic Field Around a Current-Carrying Wire

When a current flows through a conducting wire, a magnetic field is produced around the wire.
The field pattern is made up of concentric circles around the wire, showing the field has no poles.
The field is strongest closest to the wire and gets weaker as the distance from the wire increases — the circles get further apart.
The direction of the field can be found using the right-hand thumb rule: point your thumb in the direction of the current, and your fingers curl in the direction of the magnetic field.
Reversing the current reverses the direction of the magnetic field.
If there is no current, there is no magnetic field.
Increasing the current increases the strength of the magnetic field, making the field lines closer together.

The direction of the magnetic field around a current-carrying wire, found using the right-hand grip rule.

Magnetic Field Around a Solenoid

A solenoid is a coil of wire. The magnetic field lines around each loop add together, passing through the centre of the coil.
The magnetic field around a solenoid is similar to that of a bar magnet, with one end acting as a north pole and the other as a south pole.
Inside the solenoid, the magnetic field is strong and uniform (same strength and direction at all points).
To find the polarity of the ends, view the solenoid from one end: if the current flows clockwise, that end is the south pole; if anticlockwise, it is the north pole.
If the current direction changes, the north and south poles are reversed.
If there is no current, there is no magnetic field around or through the solenoid.

Increasing the Strength of a Solenoid's Magnetic Field

Increase the current flowing through the wire.
Increase the number of turns in the coil in a given length.
Reduce the length of the wire while keeping the same number of turns.
Add an iron core through the centre of the coils — the iron becomes an induced magnet, making the overall magnet much stronger.
An electromagnet is a solenoid with an iron core; its magnetic field can be switched on and off with the current.
The strength of an electromagnet can be changed by increasing or decreasing the current.

The Motor Effect

The motor effect occurs when a wire carrying a current is placed in a magnetic field and experiences a force.
It is caused by the interaction of two magnetic fields: the field around the current-carrying wire and the external magnetic field (e.g. between two magnets).
The size of the force can be increased by: increasing the current, using stronger magnets, or placing the wire at 90° to the magnetic field lines.
If the wire is parallel to the magnetic field, there is no force (F = 0).
The force is maximum when the wire is perpendicular to the field lines.

Fleming's Left-Hand Rule

Use Fleming's left-hand rule to find the direction of the force (thrust) on a current-carrying wire.
Point your First finger in the direction of the magnetic Field (N to S).
Point your seCond finger in the direction of the Current (positive to negative terminal).
Your THumb then points in the direction of the THrust (force).
The force, current and magnetic field are all perpendicular to each other.
Remember: the rule gives the direction of the force (movement), not the current or field.

Fleming's left-hand rule: thumb = force (thrust), first finger = field, second finger = current.

Calculating Magnetic Force

The force on a current-carrying conductor at right angles to a magnetic field is calculated using: F = B × I × L.
F = force in newtons (N).
B = magnetic flux density (strength of the magnetic field) in tesla (T).
I = current in amperes (A).
L = length of the conductor in the magnetic field in metres (m).
Always convert lengths from cm to m before calculating (e.g. 5 cm = 0.05 m).
Example: A 0.05 m wire with 1.5 A in a field experiences a force of 0.06 N. Then B = F / (I × L) = 0.06 / (1.5 × 0.05) = 0.8 T.

Setup for demonstrating the force on a current-carrying conductor in a magnetic field.

The Electric Motor

A simple d.c. electric motor uses the motor effect to make a coil rotate continuously in one direction.
The motor consists of a coil of wire free to rotate in a uniform magnetic field, connected to a cell via a split-ring commutator and carbon brushes.
Current in the coil produces a magnetic field that interacts with the external field, exerting forces on the sides of the coil.
The forces act in opposite directions on each side of the coil, causing it to rotate.
When the coil is vertical, the split ring is not in contact with the brushes, so no current flows and no forces act — but momentum carries it past this point.
The split-ring commutator reverses the current every half turn, so the coil continues to rotate in the same direction.
To increase the speed of rotation: increase the current or use a stronger magnet.
To change the direction of rotation: reverse the current supply or reverse the magnetic field (swap the poles).
To increase the force supplied by the motor: increase the current, increase the magnetic field strength, or add more turns to the coil.

Structure of a simple d.c. motor, showing the coil, split-ring commutator, carbon brushes and magnetic field.

Loudspeakers and Headphones

Loudspeakers and headphones convert electrical signals into sound waves using the motor effect.
A loudspeaker has a coil of wire wrapped around one pole of a permanent magnet.
An alternating current passes through the coil, creating a changing magnetic field around it.
This changing field interacts with the field from the permanent magnet, exerting a force on the coil.
The direction of the force can be found using Fleming's left-hand rule.
As the current constantly changes direction, the force on the coil constantly changes direction, making the coil oscillate.
The oscillating coil makes the speaker cone oscillate, which makes the air oscillate, creating sound waves.
Headphones are essentially small moving-coil loudspeakers and work in the same way.

ஸ்லைடுகள்

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பயிற்சி கேள்விகள்

இலவச முன்னோட்டம் — 62-இல் 8 கேள்விகள். அனைத்தையும் பார்க்க பதிவு செய்யவும்.

1.What happens when a current flows through a conducting wire?
Easy
- AA magnetic field is produced around the wire
- BThe wire becomes magnetic only if it is made of iron
- CA magnetic field is produced only inside the wire
- DNo magnetic field is produced unless there is an iron core
2.What is the shape of the magnetic field lines around a long straight current-carrying wire?
Easy
- AConcentric circles around the wire
- BStraight lines parallel to the wire
- CStraight lines radiating out from the wire
- DEllipses along the length of the wire
3.The magnetic field around a straight current-carrying wire is strongest closest to the wire and gets weaker as the distance from the wire increases.
Easy
True or false?
4.Which change will increase the strength of the magnetic field produced around a straight current-carrying wire?
Medium
- AIncreasing the current in the wire
- BIncreasing the distance from the wire
- CReversing the direction of the current
- DUsing a longer piece of wire
5.The magnetic field around a solenoid is most similar to the magnetic field of which object?
Easy
- AA bar magnet
- BA straight current-carrying wire
- CA single flat circular coil
- DA uniform field with no poles
6.Which of the following will increase the strength of the magnetic field produced by a solenoid? (select all that apply)
Medium
- AIncreasing the current through the coil
- BIncreasing the number of turns in the coil in a given length
- CAdding an iron core through the centre of the coils
- DReversing the direction of the current
- EIncreasing the length of the wire while keeping the number of turns the same
7.The magnetic field inside a solenoid is strong and uniform.
Easy
True or false?
8.What is an electromagnet?
Easy
- AA solenoid with an iron core
- BA permanent bar magnet
- CA solenoid with no core
- DA coil of wire with no current flowing

மேலும் கேள்விகள்

9.A solenoid is viewed from one end and the current is seen to travel around it in a clockwise direction. Which pole is at that end?
Medium
- ASouth pole
- BNorth pole
- CIt has no pole at that end
- DIt is impossible to tell without knowing the current direction
10.The motor effect occurs when:
Medium
- AA current-carrying wire is placed in a magnetic field and experiences a force
- BA wire is placed in a magnetic field with no current flowing
- CA current-carrying wire is placed parallel to the magnetic field lines
- DA magnet is placed near a wire with no current flowing
11.Which of the following increase the size of the force on a current-carrying wire in a magnetic field? (select all that apply)
Medium
- AIncreasing the current through the wire
- BUsing stronger magnets
- CPlacing the wire at 90° to the magnetic field lines
- DPlacing the wire parallel to the magnetic field lines
- EReversing the direction of the current
12.If a current-carrying wire is parallel to the magnetic field lines, the force on the wire is at its maximum.
Easy
True or false?
13.Which of the following is the correct equation for the force on a current-carrying conductor in a magnetic field?
Medium
- AF = B × I × L
- BF = B × I ÷ L
- CF = B ÷ (I × L)
- DF = I × L ÷ B
14.A current-carrying wire is placed in a magnetic field. The direction of the force on the wire depends on:
Medium
- AThe direction of the current and the direction of the magnetic field
- BThe direction of the current only
- CThe direction of the magnetic field only
- DThe size of the current only
15.In a simple d.c. electric motor, what is the function of the split-ring commutator?
Medium
- AIt reverses the direction of the current through the coil every half turn
- BIt increases the size of the current in the coil
- CIt reverses the direction of the magnetic field every half turn
- DIt stops the current completely so the coil can slow down
16.In a d.c. electric motor, no force acts on the coil when it is in the vertical position.
Easy
True or false?
17.How can the speed of rotation of the coil in a simple d.c. motor be increased?
Medium
- AIncrease the current or use a stronger magnet
- BReverse the direction of the current
- CReverse the poles of the magnet
- DAdd more brushes to the commutator
18.A moving-coil loudspeaker works because:
Medium
- AAn alternating current in the coil produces a changing force that makes the coil oscillate
- BA steady direct current in the coil produces a constant force that pushes the cone out once
- CThe permanent magnet attracts the coil and holds it in place
- DThe coil heats up and expands, pushing the cone
19.Which of the following statements about the magnetic field around a long straight current-carrying wire are correct? (select all that apply)
Medium
- AThe field lines form concentric circles around the wire
- BThe field is strongest closest to the wire
- CThe field lines get closer together as the distance from the wire increases
- DReversing the current reverses the direction of the magnetic field
- EThe field has a north pole and a south pole
20.Match each quantity in the equation F = BIL to its unit.
Medium
- Force (F)
- Magnetic flux density (B)
- Current (I)
- Length (L)
- newton (N)
- tesla (T)
- ampere (A)
- metre (m)
21.Place the steps for using Fleming's left-hand rule in the correct order to find the direction of the force on a current-carrying wire.
Medium
- Point the first finger in the direction of the magnetic field (N to S)
- Rotate the hand so the second finger points in the direction of the current
- The thumb points in the direction of the force (thrust)
22.A current-carrying coil in a magnetic field is used to make an electric motor. Which changes will increase the speed at which the coil rotates? (select all that apply)
Medium
- AIncreasing the current in the coil
- BUsing a stronger magnet
- CReversing the direction of the current supply
- DAdding more turns to the coil
23.In a moving-coil loudspeaker, what causes the cone to oscillate and produce sound waves?
Medium
- AThe coil experiences a changing force due to the alternating current in the magnetic field
- BThe permanent magnet vibrates and pushes the cone
- CThe alternating current directly heats the cone, making it expand and contract
- DThe coil rotates continuously like a motor
24.A current-carrying conductor is placed in a magnetic field. The direction of the force on the conductor depends on:
Medium
- AThe direction of the current and the direction of the magnetic field
- BThe size of the current and the strength of the magnetic field only
- CThe length of the conductor and the size of the current only
- DThe direction of the current only
25.A student reads a magnetic field strength of 8.1 mT at a distance of 1.0 cm from a long straight current-carrying wire. What is the most likely reading at a distance of 2.0 cm from the same wire, assuming the current is unchanged?
Medium
- A16.2 mT
- B3.9 mT
- C8.1 mT
- D0.81 mT
26.A metal roller of length 0.060 m carrying a current of 2.5 A sits at 90° to a magnetic field of flux density 1.2 T. What is the force on the roller?
Medium
- A0.18 N
- B1.8 N
- C0.018 N
- D180 N
27.A 5 cm length of wire is at 90° to a magnetic field. When a current of 1.5 A flows through the wire it experiences a force of 0.06 N. What is the magnetic flux density of the magnet?
Hard
- A0.8 T
- B0.008 T
- C8 T
- D0.45 T
28.For a current-carrying conductor, the force is maximum when the conductor is parallel to the magnetic field lines.
Easy
True or false?
29.In a moving-coil loudspeaker, an alternating current makes the coil oscillate because the force on the coil keeps changing direction.
Medium
True or false?
30.A current-carrying wire is placed between the poles of a magnet. Which changes will increase the size of the force on the wire? (select all that apply)
Medium
- AIncreasing the current in the wire
- BUsing a stronger magnet
- CTurning the wire so it is parallel to the field lines
- DIncreasing the length of wire inside the magnetic field
- EReversing the direction of the current
31.A student is analysing a simple d.c. electric motor. Which statements about the split-ring commutator are correct? (select all that apply)
Hard
- AIt reverses the direction of the current through the coil every half turn
- BIt keeps the coil rotating in the same direction
- CIt is a circular tube of metal split in two
- DIt increases the magnetic flux density of the field
- EIt stops the current flowing through the coil at all times
32.Match each part of a simple d.c. electric motor to its function.
Medium
- Coil of wire
- Split-ring commutator
- Carbon brushes
- Magnet
- Carries the current that experiences the force
- Reverses the current every half turn
- Make electrical contact with the split ring
- Provides the uniform external magnetic field
33.Place the stages of how a moving-coil loudspeaker produces sound in the correct order.
Medium
- An alternating current passes through the coil
- A changing magnetic field is produced around the coil
- The coil's field interacts with the permanent magnet's field
- A force that keeps changing direction acts on the coil
- The coil and cone oscillate, making the air vibrate
34.The current is doubled and the length of wire in the field is halved. What happens to the force on the wire?
Hard
- AIt stays the same
- BIt doubles
- CIt halves
- DIt becomes four times larger
35.A student sets up a wire between the poles of a horseshoe magnet so that the wire is horizontal and the magnetic field is also horizontal. The current flows to the right. In which direction does the wire experience a force?
Medium
- AThere is no force on the wire
- BUpwards
- CDownwards
- DInto the page
36.A current-carrying wire is placed at 90° to a uniform magnetic field. The current is 2.0 A, the length of wire in the field is 0.50 m and the magnetic flux density is 0.20 T. What is the force on the wire?
Medium
- A0.20 N
- B0.40 N
- C2.0 N
- D0.10 N
37.A student sets up a simple d.c. motor and observes that the coil rotates. They then reverse the connections to the battery. What happens to the coil?
Hard
- AIt rotates in the opposite direction
- BIt rotates in the same direction but faster
- CIt stops rotating
- DIt rotates in the same direction but slower
38.Which of the following changes would increase the size of the force on a current-carrying wire in a magnetic field? (select all that apply)
Medium
- AIncreasing the current in the wire
- BUsing a stronger magnet
- CPlacing the wire at 90° to the magnetic field lines
- DPlacing the wire parallel to the magnetic field lines
- EDecreasing the length of wire in the magnetic field
39.In a moving-coil loudspeaker, the coil oscillates because the force on it changes direction as the alternating current changes direction.
Easy
True or false?
40.Match each component of a simple d.c. electric motor to its function.
Medium
- Split-ring commutator
- Carbon brushes
- Coil of wire
- Reverses the current direction every half turn
- Connect the rotating coil to the external circuit
- Carries current and experiences forces causing rotation
41.A wire of length 0.20 m carrying a current of 3.2 A is at 90° to a magnetic field of flux density 0.05 T. Calculate the force on the wire.
Medium
42.The magnetic flux density at a metal roller is 1.2 T and the current in the roller is 2.5 A. The length of the roller carrying the current is 0.060 m. Calculate the force on the roller.
Medium
43.Complete the sentence about the motor effect.
Easy
In Fleming's left-hand rule, the first finger points in the direction of the magnetic ____, the second finger points in the direction of the ____, and the thumb points in the direction of the ____.
44.In a loudspeaker, what is the name of the component that oscillates to produce the sound waves?
Easy
45.A straight wire of length 0.15 m carrying a current of 4.0 A is placed at 90° to a uniform magnetic field of flux density 0.25 T. Calculate the force on the wire.
Medium
46.A current of 2.5 A flows in the left side of a coil that is 0.10 m long. The magnetic flux density is 0.10 T. Calculate the force on the left side of the coil, in newtons.
Medium
47.A wire of length 0.30 m carrying a current of 2.0 A is placed at 90° to a uniform magnetic field. The force on the wire is 0.45 N. Calculate the magnetic flux density of the field, in tesla.
Hard
48.Complete the sentences about the force on a current-carrying conductor using the equation F = BIl.
Medium
In the equation F = BIl, B stands for magnetic ____ density, measured in ____, and l is the length of the conductor in ____.
49.In a moving-coil loudspeaker, what is the name of the component that oscillates to produce the sound waves?
Medium
50.Calculate the force on the wire, in newtons.
Medium
51.The wire is turned so that it is parallel to the magnetic field lines. What is the force on the wire now, in newtons?
Medium
52.A wire of length 0.25 m carrying a current of 3.0 A is placed at 90° to a magnetic field of flux density 0.40 T. Calculate the force on the wire, in newtons.
Medium
53.Explain why a force acts on a coil of wire when a current passes through it in a magnetic field.
Hard
54.Describe how Fleming's left-hand rule can be used to determine the direction of the force acting on a current-carrying conductor in a magnetic field.
Medium
55.Explain how the split-ring commutator ensures that the coil in a simple d.c. electric motor continues to rotate in the same direction.
Hard
56.A wire of length 0.20 m carrying a current of 3.2 A is at 90° to a magnetic field of flux density 0.05 T. Calculate the force on the wire.
Medium
- A1.032 N
- B0.032 N
- C2.032 N
- D-0.968 N
57.The magnetic flux density at a metal roller is 1.2 T and the current in the roller is 2.5 A. The length of the roller carrying the current is 0.060 m. Calculate the force on the roller.
Medium
- A1.18 N
- B2.18 N
- C0.18 N
- D-0.82 N
58.A straight wire of length 0.15 m carrying a current of 4.0 A is placed at 90° to a uniform magnetic field of flux density 0.25 T. Calculate the force on the wire.
Medium
- A0.15 N
- B2.15 N
- C1.15 N
- D-0.85 N
59.A current of 2.5 A flows in the left side of a coil that is 0.10 m long. The magnetic flux density is 0.10 T. Calculate the force on the left side of the coil, in newtons.
Medium
- A0.025 N
- B1.025 N
- C-0.975 N
- D2.025 N
60.A wire of length 0.30 m carrying a current of 2.0 A is placed at 90° to a uniform magnetic field. The force on the wire is 0.45 N. Calculate the magnetic flux density of the field, in tesla.
Hard
- A-0.25 T
- B0.75 T
- C1.75 T
- D2.75 T
61.A wire of length 0.20 m carries a current of 4.0 A at right angles to a magnetic field of flux density 0.15 T. Calculate the force on the wire, in newtons.
Medium
- A0.12 N
- B-0.88 N
- C2.12 N
- D1.12 N
62.A wire of length 0.25 m carrying a current of 3.0 A is placed at 90° to a magnetic field of flux density 0.40 T. Calculate the force on the wire, in newtons.
Medium
- A0.3 N
- B2.3 N
- C-0.7 N
- D1.3 N

ஃப்ளாஷ் கார்டுகள்

What is produced around a conducting wire when a current flows through it?

A magnetic field is produced around the wire. If there is no current flowing, there is no magnetic field.

What shape is the magnetic field pattern around a straight current-carrying wire?

It is made up of concentric circles around the wire. A circular field pattern shows the field has no poles.

How does the strength of the magnetic field change with distance from a straight current-carrying wire?

The field is strongest closest to the wire and gets weaker as the distance increases. The circles get further apart as you move away from the wire.

What two factors affect the strength of the magnetic field around a straight wire?

The size of the current and the distance from the wire. A larger current gives a stronger field; a greater distance gives a weaker field.

What happens to the magnetic field around a wire if the direction of the current is reversed?

The direction of the magnetic field is reversed. The field pattern stays the same shape but points the opposite way.

What rule gives the direction of the magnetic field around a current-carrying wire?

The right-hand thumb rule. Point the thumb in the direction of the current and the fingers curl in the direction of the magnetic field.

What is a solenoid?

A wire coiled into a loop or coil. Coiling the wire increases the strength of the magnetic field created by the current.

What is the shape of the magnetic field around a solenoid similar to?

It is similar to the field of a bar magnet. One end behaves like a north pole and the other like a south pole.

Describe the magnetic field inside a solenoid.

It is strong and uniform. The fields from the individual turns add together along the centre of the solenoid.

How do you work out the polarity of the ends of a solenoid?

View the solenoid from the end. Clockwise current means that end is the south pole; anticlockwise current means that end is the north pole.

Give three ways to increase the strength of the magnetic field around a solenoid.

Increase the current, increase the number of turns in a given length, or add an iron core through the centre of the coils.

What is an electromagnet?

A solenoid with an iron core. Its magnetic field can be switched on and off with the current, and its strength can be changed by changing the current.

Why does adding an iron core increase the strength of a solenoid's magnetic field?

The iron core becomes an induced magnet when current flows through the coils. The field from the solenoid and the iron core together make a much stronger magnet.

What is the motor effect?

When a wire carrying a current is placed in a magnetic field, it experiences a force. It happens because the field around the wire interacts with the external magnetic field.

Why does a current-carrying wire experience a force in a magnetic field?

Two magnetic fields interact: the field produced around the wire by the current and the external magnetic field it is placed in. The interaction produces a force on the wire.

State three ways to increase the size of the force on a current-carrying wire in a magnetic field.

Increase the current, use stronger magnets, and place the wire at 90° to the magnetic field lines. The force is maximum when the field and current are perpendicular.

What is the force on a current-carrying wire when it is parallel to the magnetic field lines?

The force is zero. There is no interaction between the two magnetic fields when they are parallel.

Write the equation for the force on a current-carrying conductor at right angles to a magnetic field.

F = B × I × l, where F is force in newtons (N), B is magnetic flux density in tesla (T), I is current in amps (A) and l is length in metres (m).

What does the symbol B represent in the equation F = BIl, and what is its unit?

B is the magnetic flux density, which is the strength of the magnetic field. It is measured in tesla (T).

What must you remember to do to the length before using F = BIl?

Convert it to metres. For example, 5 cm must be written as 0.05 m.

What does Fleming's left-hand rule determine?

The direction of the force (thrust) on a current-carrying wire in a magnetic field. The force, current and magnetic field are all perpendicular to each other.

How do you use Fleming's left-hand rule?

Point the First finger in the direction of the Field, the seCond finger in the direction of the Current, and the THumb gives the direction of the THrust (force).

In Fleming's left-hand rule, which direction does the magnetic field always point?

From north to south. Current is always taken as flowing from the positive terminal to the negative terminal.

What is the basis of a simple d.c. electric motor?

A coil of wire carrying a current in a magnetic field tends to rotate. Forces act in opposite directions on each side of the coil, making it spin in one direction.

What is the job of the split-ring commutator in a d.c. motor?

It reverses the direction of the current through the coil every half turn. This keeps the coil rotating in the same direction.

Why does no force act on the coil when it is vertical in a d.c. motor?

The split ring is not in contact with the brushes, so no current flows through the coil. The coil keeps turning because of its momentum.

Give two ways to increase the speed of rotation of a d.c. motor's coil.

Increase the current, or use a stronger magnet. Adding more turns to the coil also increases the force supplied by the motor.

How can the direction of rotation of a d.c. motor be reversed?

Reverse the direction of the current supply, or reverse the direction of the magnetic field by swapping the poles of the magnet.

How does a moving-coil loudspeaker produce sound?

An alternating current in the coil creates a changing magnetic field that interacts with the permanent magnet's field. The force on the coil changes direction, making the coil and cone oscillate and creating sound waves.

Why does the coil in a loudspeaker oscillate?

The current is constantly changing direction, so the magnetic field around the coil keeps changing. The force on the coil therefore keeps changing direction, making it oscillate.

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இந்த தலைப்பிற்கான ஒவ்வொரு கேள்வியையும், ஸ்லைடுகளையும், ஃப்ளாஷ் கார்டுகளையும் மற்றும் திருப்புதல் குறிப்புகளையும் பார்க்க இலவச கணக்கை உருவாக்கவும்.

பதிவு செய்க — இலவசம்உள்நுழைக

முந்தைய தேர்வுகள்

இந்த தலைப்பிற்கான முந்தைய தேர்வு பயிற்சி விரைவில் வருகிறது.

விரைவில் வருகிறது