P4 Flashcards
What poles do all magnets have?
North and south poles.
What is a magnetic field?
A region where magnetic material (like iron, nickel, or cobalt) experiences a force.
How are magnetic field lines used in diagrams?
They show the direction and strength of the magnetic field, flowing from north to south outside the magnet.
What does it mean if magnetic field lines are close together?
The magnetic field is stronger.
What is magnetic flux density
It is a measure of the strength of the magnetic field, in teslas (T).
How do two permanent bar magnets affect each other’s magnetic fields?
When placed near each other, they create a combined magnetic field pattern.
How can you use iron filings to see a magnetic field pattern?
Sprinkle iron filings around a magnet, and they gather along the field lines, showing the magnetic pattern.
How does using a compass help you see a magnetic field pattern?
Place a compass near the magnet; the needle aligns with the magnetic field direction, helping trace the field lines.
What can you do to create a permanent record of a magnetic field pattern using paper and iron filings?
Place paper over the magnet, sprinkle filings, and tap gently. Use glue to fix the pattern for a permanent visual.
Describe the plotting compass method for mapping out a magnetic field.
Move a plotting compass around the magnet, marking the needle’s position at each point to draw the magnetic field lines.
Why is it difficult to remove all traces of a magnetic field from iron filings after removing the magnet?
filings retain some magnetism, creating a “memory” of the field pattern even after the magnet is removed.
How can you prove the Earth has a magnetic field using a compass?
Compasses always point north-south even when far from other magnets, showing that Earth has its own magnetic field
What happens when like poles of two magnets are brought near each other?
They repel each other.
What happens when opposite poles of two magnets are brought near each other?
They attract each other
How does a material become magnetized by a nearby magnet?
A magnetic material becomes a temporary magnet when near a magnet, aligning with the field, but loses magnetism when the field is removed.
What happens when an unmagnetized material is placed in a strong magnetic field?
It can become magnetized, temporarily or permanently, depending on the material.
How does the distance between two magnets affect their force of attraction or repulsion?
The closer they are, the stronger the force; the force decreases quickly with increased distance.
Why might two magnets attract or repel even when one is not visibly magnetic?
An unmagnetized material can be temporarily magnetized by a nearby magnet, creating attraction or repulsion.
How does a current-carrying wire affect its surroundings?
It produces a magnetic field around it.
What happens to the magnetic field when you increase the electric current through a wire?
The magnetic field strength increases.
What is the shape of the magnetic field around a straight, current-carrying wire?
Concentric circles form around the wire.
How can you determine the direction of the magnetic field around a current-carrying wire?
Use the right-hand rule: if you point your thumb in the direction of the current, your fingers curl in the direction of the magnetic field.
What happens to the magnetic field strength as you move further from the current-carrying wire?
The field strength decreases.
How does the magnetic field around a flat circular coil resemble that of a bar magnet?
The magnetic field in the center of the coil resembles the field around a bar magnet, with circular field lines around the coil.
What is a solenoid, and what is its magnetic field like?
A solenoid is a coil of wire with a strong, uniform magnetic field inside, similar to a bar magnet.
How can the magnetic field strength of a solenoid be increased?
Increase the current, add more turns to the coil, or insert an iron core.
How does inserting an iron core affect the magnetic field of a solenoid?
It increases the strength of the magnetic field and makes the solenoid an electromagnet.
What factors increase the magnetic effect at the ends of a solenoid?
Higher current, more turns in the coil, and the presence of an iron core.
What happens when a current-carrying conductor is placed in a magnetic field?
The magnetic fields from the wire and the magnets combine, resulting in a force on the wire.
Under what condition does a current-carrying wire experience no force in a magnetic field?
If the wire is aligned along the magnetic field lines, it won’t experience any force.
How can the force on a current-carrying wire be increased?
By increasing the current, using a stronger magnetic field, or adjusting the angle of the wire so it is perpendicular to the magnetic field lines.
How does the angle of the wire relative to the magnetic field affect the force it experiences?
The force is strongest when the wire is at a 90° angle to the magnetic field and weakens as the angle decreases.
In which direction does the force act on a current-carrying conductor in a magnetic field?
The force acts perpendicular to both the direction of the current and the magnetic field
How is a horseshoe magnet typically used to demonstrate this force?
The wire is placed between the poles of the horseshoe magnet, where the magnetic field is strong, causing the wire to experience a force when current is applied.
What is Fleming’s left-hand rule used for?
It is used to find the direction of the force on a current-carrying conductor in a magnetic field.
How do you apply Fleming’s left-hand rule?
. First finger points in the direction of the magnetic field (from north to south).
• Second finger points in the direction of the current (from positive to negative).
• Thumb points in the direction of the force (motion).
What does magnetic flux density (B) represent in this formula?
It is a measure of the strength of the magnetic field.
Why should you remember that magnetic flux density is just a fancy term for magnetic field strength?
It simplifies your understanding of
How does a simple electric motor work with a current-carrying coil?
The coil is placed between opposite poles of a magnet, and the forces on each side of the coil cause it to spin on its axis.
Why does the coil in an electric motor continue rotating in one direction?
A split-ring commutator reverses the current every half-turn to keep the motor rotating in the same direction.
How can you increase the speed of a simple electric motor?
Increase the current, use a stronger magnetic field, or increase the magnetic flux density.
How can Fleming’s left-hand rule help determine the rotation direction in a motor?
Draw arrows for the magnetic field and current directions on each side of the coil, and use Fleming’s left-hand rule to check if it will rotate clockwise or counterclockwise.
How does a loudspeaker produce sound using a coil and a magnet?
A current flows through the coil, creating a magnetic field that interacts with the magnet’s field, causing the coil to move.
What happens when the current in a loudspeaker coil changes direction?
The direction of the force on the coil reverses, causing it to move back and forth.
How does the movement of the coil in a loudspeaker produce sound?
The moving coil makes a cone vibrate, creating sound waves in the air.
What causes the pitch of the sound produced by a loudspeaker to change?
Variations in the frequency of the electrical current change the speed of cone vibrations, producing different sounds.
How can a potential difference be induced in a conductor?
A potential difference is induced when a conductor cuts through magnetic field lines, or when there is a change in the magnetic field around a conductor.
What is electromagnetic induction?
Electromagnetic induction is the process of inducing a potential difference in a conductor due to a changing magnetic field.
What happens if the conductor is part of a complete circuit?
If the conductor is part of a complete circuit, a current is induced, generating electricity
How can the size of the induced potential difference be increased?
Increase the speed of movement, use a stronger magnet, or increase the number of turns on the coil.
What happens to the direction of the induced current if the movement direction or magnetic field polarity is reversed?
The direction of the induced current also reverses.
What happens when the conductor cuts through the magnetic field lines faster?
A larger potential difference is induced.
How does a microphone use electromagnetic induction?
Sound waves hit the diaphragm, causing it to move. The coil of wire attached to the diaphragm moves in the magnetic field, inducing a current that varies with the sound wave’s frequency and amplitude.
What varies with the frequency and amplitude of the sound wave in a microphone?
The induced current.
How does a dynamo generate direct current (DC)?
A dynamo has a coil that rotates in a magnetic field, inducing a potential difference in the coil. The split-ring commutator ensures the current flows in one direction, producing direct current.
What type of current does a dynamo produce?
Direct current (DC).
What component ensures the current flows in one direction in a dynamo?
The split-ring commutator.
How does an alternator generate alternating current (AC)?
An alternator uses a rotating coil in a magnetic field with slip rings that allow the current to alternate as the coil spins, producing AC.
What type of current does an alternator produce?
Alternating current (AC)
What is the role of slip rings in an alternator?
Slip rings allow the current to alternate, producing an AC output.
How can you determine the direction of current in the coil of a dynamo or alternator?
Use Fleming’s right-hand rule.
What is a transformer used for?
To change the potential difference of an alternating current.
How does a transformer work?
An alternating current in the primary coil creates a changing magnetic field in the iron core, which induces an alternating potential difference in the secondary coil.
Why do transformers require alternating current?
An alternating current is needed to create a changing magnetic field, which is essential for inducing a potential difference in the secondary coil.
What are the main components of a transformer?
Primary coil, secondary coil, and an iron core.
Why is an iron core used in transformers?
To increase the strength of the magnetic field.
What is a step-up transformer?
A step-up transformer increases the potential difference, with more turns on the secondary coil than on the primary coil.
What is a step-down transformer?
A step-down transformer decreases the potential difference, with fewer turns on the secondary coil than on the primary coil.
Why are step-up transformers used in power stations?
To increase the potential difference, reducing energy loss during transmission over long distances.
Why are step-down transformers used in homes?
To reduce the potential difference to a safer level for domestic use.
Why does a complete circuit need to be present for current to be induced?
Without a complete circuit, electrons cannot flow, and thus no current is produced even if a potential difference is induced.
What does increasing the speed of the coil’s rotation do in a generator?
It increases the potential difference and the frequency of the alternating current produ
What is the role of alternating current (AC) in transformers?
AC allows the magnetic field to constantly change, which is necessary for inducing a potential difference in the secondary coil.
