| What is the conventional current? | The conventional current is the flow of current from the positive terminal through the circuit, into the negative terminal. The reverse of normal electron flow. |
| Where is the magnetic field produced when a current flows through a conducting wire? | When a current flows through a conducting wire, the magnetic field is produced around the wire. |
| How can you prove there is a magnetic field around the wire? | You can prove there is a magnetic field around the wire using a compass.
When the current is turned off the compass needle aligns with the Earth’s magnetic field, but when the current is turned on the compass needle deflects, proving there is a magnetic field around the wire. |
| What does the strength of a magnetic field depend on? | The strength of a magnetic field depends on the size of the current, and the distance of a magnetic field from the wire. A larger current produces a stronger magnetic field and a magnetic field closer to the wire is stronger, because the magnetic field decreases the further away from the wire. |
| What happens when the direction of the current is changed? | When the direction of the current is changed, the direction of the magnetic field is also changed. If the direction of the conventional current is reversed, the direction of the magnetic field will also reverse. So if a compass were placed near the wire, it would reflect in the opposite direction to before. |
| How can you increase the strength of the wire? | You can increase the strength of the magnetic field by coiling the wire, and this shape is called a solenoid. Solenoids increase the strength because when the current is turned on, a strong and uniform magnetic field is produced inside the solenoid. |
| What does the magnetic field around a solenoid have a similar shape to? | The magnetic field around a solenoid has a similar shape to the magnetic field around a bar magnet. |
| How do you use the right-hand rule to find the direction of the magnetic field produced by a wire and a solenoid? | You can use the right-hand grip rule to find the direction of the magnetic field produced by a wire by making a thumbs-up motion, where the thumb points in the direction of the conventional current and the fingers point in the direction of the magnetic field.
Use the right-hand rule to find the direction of the magnetic field produced by a solenoid by placing your fingers in a first so they point in the same direction as the conventional current, while your thumb points in the direction of the north pole. |
| How can the strength of a magnetic field produced by a solenoid be increased? | The strength of a magnetic field produced by a solenoid can be increased by increasing the size of the current. Increasing the current increases the size of the magnetic field which increases the number of turns in the coil. So the magnetic field has greater strength than a coil with fewer turns.
And the strength of the magnetic field can be increased by creating an iron core, to do this place a piece of iron in the solenoid. |
| What is an electromagnet, a magnetic field and magnetic flux density? | An electromagnetic is a solenoid that contains an iron core.
A magnetic field is the region around a magnet where a force acts on another magnet or magnetic material.
And the magnetic flux density is the measure of the strength of the magnetic field. |
| Why are electromagnets useful? | Electromagnets are useful because the strength of the magnetic field can be changed by changing the size of the current. Electromagnets can also be turned on and off. |
| What does the arrow of a diagram that represents a wire carrying an electric current show? | The arrow of a diagram that represents a wire carrying an electric current shows the direction of the conventional current (there are also magnetic fields around the wire which is not shown). |
| What happens when a wire is placed in a magnetic field? | When a wire is placed in a magnetic field, the magnetic field around the wire interacts with the magnetic field between the magnets. This causes the wire to experience a force. As in this case, the force is a forward direction, the force causes the wire to move upwards. This is called the motor effect. |
| How can the size of a force be calculated? | The size of a force can be calculated using the equation F = B x I x l
Force (N) = magnetic flux density (Tesla) x current (A) x length (m) |
| What does the size of a force equation apply to? | The size of force applies to a wire that is at right angles to the magnetic field. |
| What does the force depend on? | The force depends on the magnetic flux density, the current, and the length of the wire. |
| How can you use Fleming’s left-hand rule to find the direction of a force? | To use Fleming’s left-hand rule to find the direction of a force, point your thumb, forefinger, and middle finger so they all form right angles, ensuring that your forefinger points in the direction of the magnetic field from North to South, point your middle finger in the direction of the conventional current (+ to –), and point your thumb in the direction of the motion (force) |
| When will the magnetic field not experience a force? | The magnetic field will not experience a force when the conductor is parallel to the magnetic field |
| What is a moment? | A moment is the turning effect of a force. |
| When will a loop rotate in a clockwise direction? | A loop will rotate in a clockwise direction when a loop of wire carrying a current has the current running in opposite directions on either side of the loop, e.g. on the left, the current runs back to front, but on the right, it runs front to back.
Then the loop is placed in a magnetic field where it experiences a force on the left, that acts up, and force on the right that acts down.
Therefore a moment is created on the left and a moment is created on the right, so it rotates in a clockwise direction.
But it will stop rotating when it reaches 90 degrees. |
| What would happen if the loop rotated beyond 90 degrees? | If the loop rotated beyond 90 degrees the direction of the current would cause the force on the left to act downward and the force on the right to act upwards, so they push the loop back to the 90 degrees position.
This can be stopped by switching the direction of the current when the loop passes 90 degrees, using a split-ring commutator. |
| How is a split-ring commutator used to switch the direction of the current? | A split-ring commutator is used to switch the direction of the current.
A commutator is a split metal ring connected to conducting brushes that allow the electric current to pass into the ring.
When the current produces a turning force of the motor, it causes the motor to rotate in a clockwise direction. This allows the current to be broken for a fraction of a second.
However, momentum causes the wire to keep turning, which allows the current to switch direction. So the force on the left still acts upwards and the force on the right still acts downwards. Therefore the commutator allows the motor to keep turning in the same direction. |
