Electromagnetism — AQA GCSE Combined Science
Test yourself on Electromagnetism with AQA GCSE practice questions.
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Electromagnetism explained
A current-carrying conductor is surrounded by a magnetic field.
Read the full explanation
You can detect it by placing a plotting compass near a straight wire: when the current is switched on, the compass needle deflects, showing a field is present. The field forms concentric circles around the wire, with the direction given by the right-hand grip rule: point your right thumb along the conventional current, and your curled fingers show the field direction. Field strength increases when the current increases, and decreases as you move further from the wire. Reversing the current reverses the field direction. This principle underpins electromagnets, motors and transformers, so understanding how current and distance affect the field is essential.
Shaping a wire to form a solenoid increases the strength of the magnetic field created by a current through the wire. The magnetic field inside a solenoid is strong and uniform.
A solenoid is a coil of insulated wire, often wound around a soft iron core. Winding a current-carrying wire into a solenoid concentrates the magnetic field lines inside the coil, making the field much stronger than around a straight wire carrying the same current. Inside the solenoid, the field lines are parallel and evenly spaced, so the field is strong and uniform. Outside, the field resembles that of a bar magnet, with a north and south end. Adding more turns, increasing the current, or inserting a soft iron core further strengthens the field. This makes solenoids useful in electromagnets, relays and loudspeakers.
The magnetic field around a solenoid has a similar shape to that of a bar magnet. Adding an iron core increases the strength of the magnetic field of a solenoid. An electromagnet is a solenoid with an iron core.
A solenoid is a long coil of insulated wire. When current flows, each turn produces a field; inside the coil these fields combine into a strong, uniform field along the axis, while outside the pattern resembles the field of a bar magnet, with field lines emerging from one end and entering the other. The end from which field lines emerge acts as a north pole. Reversing the current reverses the poles. Inserting a soft iron core concentrates and strengthens the field because iron is easily magnetised, so the solenoid becomes an electromagnet. Unlike a permanent bar magnet, an electromagnet can be switched on and off and its strength changed by altering current or number of turns.
describe how the magnetic effect of a current can be demonstrated
When a current flows through a conductor, a magnetic field forms around it. This is the magnetic effect of a current. To demonstrate it, place a straight wire through a horizontal card and connect it to a battery and switch. Sprinkle iron filings on the card and tap gently; the filings form concentric circles around the wire. A plotting compass placed near the wire also shows the field direction. Reversing the battery reverses the current and reverses the field direction. Increasing the current strengthens the field, shown by a denser pattern. The same effect can be shown with a solenoid, where the field resembles a bar magnet. The demonstration therefore links current, magnetic field and direction, and shows that the effect is temporary and disappears when the current stops.
draw the magnetic field pattern for a straight wire carrying a current and for a solenoid (showing the direction of the field)
A straight current-carrying wire has a magnetic field made of concentric circles centred on the wire. The circles lie in planes perpendicular to the wire. To show direction, use the right-hand grip rule: point the thumb of your right hand along the conventional current, and your curled fingers show the field direction. For a solenoid, the field lines outside resemble those of a bar magnet, running from the north end to the south end, while inside the solenoid the field lines are parallel and close together, running from south to north. The ends behave as north and south poles. Reversing the current reverses the field direction. When drawing, use arrows on the field lines, keep the lines smooth and non-crossing, and show the wire or solenoid clearly.
explain how a solenoid arrangement can increase the magnetic effect of the current.
A solenoid is a long coil of insulated wire. Winding the wire into a solenoid increases the magnetic effect because each turn carries the same current and produces its own magnetic field; these fields line up along the inside of the coil and add together, so the field inside is much stronger than around a single straight wire. The field pattern is like that of a bar magnet, with a north end and a south end. The effect is increased further by increasing the current, by adding more turns per unit length, and by placing a soft iron core inside the coil. The iron core becomes an induced magnet and concentrates the magnetic field lines, making the electromagnet stronger. Reversing the current reverses the magnetic poles.
Your focus
- Describe how a current-carrying wire produces a magnetic field around it.
- Explain how the strength of the magnetic field depends on current and distance from the wire.
- Apply the right-hand grip rule to determine the direction of the magnetic field around a straight wire.
Show all 18 objectives
- Describe how shaping a wire into a solenoid affects the magnetic field produced by a current.
- Explain why the magnetic field inside a solenoid is strong and uniform.
- Identify ways to increase the strength of the magnetic field of a solenoid.
- Describe the shape of the magnetic field around a current-carrying solenoid and compare it with a bar magnet's field.
- Explain how adding a soft iron core changes the strength of a solenoid's magnetic field.
- Define an electromagnet and state one advantage it has over a permanent magnet.
- Describe a practical method using iron filings or a plotting compass to show the magnetic field around a current-carrying wire.
- Explain how the pattern changes when the current is increased or reversed.
- State that the magnetic effect disappears when the current is switched off.
- Draw the magnetic field pattern around a straight current-carrying wire, including direction arrows.
- Draw the magnetic field pattern of a solenoid, showing the direction of the field inside and outside.
- Apply the right-hand grip rule to determine the direction of the magnetic field.
- Describe how winding a current-carrying wire into a solenoid increases the magnetic effect.
- Explain how current, number of turns per unit length and a soft iron core affect the strength of a solenoid's magnetic field.
- Compare the magnetic field pattern of a solenoid with that of a bar magnet.
Electromagnetism exam tips
Marking Points
- A magnetic field is produced around a conducting wire only when a current flows through it.
- The field lines around a straight wire are concentric circles centred on the wire.
- Increasing the current through the wire increases the strength of the magnetic field.
- Increasing the distance from the wire decreases the strength of the magnetic field.
- The direction of the magnetic field reverses if the direction of the current reverses.
- The right-hand grip rule predicts the field direction: thumb along conventional current, fingers curl in field direction.
- Forming a wire into a solenoid increases the strength of the magnetic field compared with a straight wire.
- The magnetic field inside a solenoid is strong and uniform.
- Inside the solenoid, field lines are parallel and evenly spaced.
- The field outside a solenoid resembles the field of a bar magnet.
- Increasing the number of turns or the current increases the field strength of a solenoid.
- Adding a soft iron core increases the strength of the magnetic field of a solenoid.
- A solenoid is a coil of insulated wire carrying a current; its field is produced only while current flows.
- Inside the solenoid the field is strong and approximately uniform along the axis; outside it resembles the field around a bar magnet.
- Field lines emerge from the north-seeking end and enter the south-seeking end; reversing current reverses the poles.
- Adding a soft iron core increases field strength because the iron becomes magnetised and adds to the field.
- An electromagnet is a solenoid with an iron core, giving a magnetic field that can be switched on and off.
- Increasing current or the number of turns per unit length increases the strength of the solenoid's field.
- A current-carrying wire produces a magnetic field around it; the field is detected using iron filings or a plotting compass.
- Iron filings sprinkled on a card around a straight wire form concentric circles centred on the wire.
- A plotting compass near the wire aligns with the field; reversing the current reverses the compass deflection.
- Increasing the current increases the strength of the magnetic field, giving a denser or more definite pattern.
- The field disappears when the current is switched off, showing the effect is due to the current, not the wire alone.
- A solenoid carrying a current produces a field pattern similar to that of a bar magnet, with a north and south end.
- For a straight wire, draw concentric circles centred on the wire, with arrows showing the field direction.
- Use the right-hand grip rule: thumb along conventional current, curled fingers give the field direction.
- For a solenoid, draw field lines outside running from the north end to the south end, like a bar magnet.
- Inside the solenoid, draw field lines parallel to the axis, running from south to north, with arrows.
- Mark the ends of the solenoid as north and south poles, and reverse them if the current is reversed.
- Ensure field lines are smooth, do not cross, and include arrows to show direction.
- A solenoid is a coil of insulated wire carrying a current, so each turn produces its own magnetic field.
- The magnetic fields from adjacent turns point in the same direction and combine, increasing the overall magnetic effect.
- The field inside the solenoid is strong and uniform, and the outside field resembles that of a bar magnet with north and south poles.
- Increasing the current increases the magnetic field strength produced by each turn.
- Increasing the number of turns per unit length increases the number of fields that combine.
- Adding a soft iron core concentrates the magnetic field lines and makes the electromagnet stronger because the iron becomes an induced magnet.
Examiner Tips
- 💡When describing the field pattern, state that the lines are concentric circles around the wire and that the spacing indicates field strength.
- 💡Use the right-hand grip rule explicitly in answers about direction, naming the thumb as current and fingers as field.
- 💡For questions comparing field strength, link your answer to both current and distance rather than only one factor.
- 💡When comparing a straight wire and a solenoid, state that the solenoid concentrates the field and makes it stronger.
- 💡Use the phrase 'strong and uniform' when describing the field inside a solenoid, and support it by referring to parallel, evenly spaced field lines.
- 💡If asked to increase the field strength of a solenoid, mention increasing current, increasing turns, or adding a soft iron core.
- 💡Sketch the field with arrows from north to south outside the coil and label the poles before writing your explanation.
- 💡When asked why an iron core helps, link it to the core becoming an induced magnet that adds to the coil's field.
- 💡Compare an electromagnet with a permanent bar magnet in terms of switching and strength control to gain comparison marks.
- 💡Name the apparatus clearly: straight wire, card, iron filings, plotting compass, battery and switch.
- 💡Describe the pattern as concentric circles around the wire, not just 'lines'.
- 💡State that reversing the current reverses the field direction, and that switching off removes the field.
- 💡Use a sharp pencil and a compass or circular object to draw neat concentric circles for the straight wire.
- 💡Label the current direction and use the right-hand grip rule to check your arrows.
- 💡For the solenoid, draw the external field like a bar magnet and add parallel internal lines with arrows.
- 💡Link each method of increasing the effect to the underlying idea that more aligned magnetic fields add together.
- 💡Use the phrase 'turns per unit length' rather than just 'more turns' when explaining the effect of coil geometry.
- 💡When describing the soft iron core, state that it becomes an induced magnet and concentrates the field lines.
Common Mistakes
- Thinking a magnetic field exists around a wire even with no current: correct this by stating that the field is produced by the current, so no current means no magnetic field.
- Believing field strength is the same everywhere around the wire: correct this by explaining that field strength decreases with distance from the wire.
- Confusing the direction of conventional current with electron flow: correct this by using conventional current from positive to negative in the right-hand grip rule.
- Thinking the field inside a solenoid is weak because it is inside the coil: correct this by stating that the field inside is strong and uniform.
- Believing the field inside a solenoid is circular like around a straight wire: correct this by describing the field inside as parallel straight lines.
- Assuming the field outside a solenoid is uniform: correct this by explaining that outside the field is like a bar magnet and is not uniform.
- Thinking the field exists only inside the solenoid: correct this by describing the external field pattern, which resembles a bar magnet's field.
- Believing any metal core strengthens the field: correct this by specifying soft iron, which is easily magnetised; materials such as copper or aluminium do not have this effect.
- Confusing the direction of field lines with the direction of current: correct this by using the right-hand grip rule to relate current direction to the field and pole positions.
- Thinking the wire itself is magnetic when no current flows; correction: the magnetic field exists only while current flows.
- Believing iron filings show the direction of the field; correction: filings show the shape, while a plotting compass shows direction.
- Assuming reversing the current has no effect; correction: reversing the current reverses the direction of the magnetic field.
- Drawing straight radial lines around a straight wire instead of concentric circles; correction: the field lines are circles centred on the wire.
- Omitting arrows on field lines; correction: arrows are needed to show the direction of the field.
- Drawing the field inside a solenoid running from north to south; correction: inside the solenoid the field runs from south to north.
- Thinking that a solenoid creates a magnetic field only when a permanent magnet is present; correction: the current itself produces the magnetic field, and a soft iron core only strengthens it.
- Believing that the magnetic field inside a solenoid is zero; correction: the field inside is strong and uniform, while the field outside is weaker and like a bar magnet's field.
- Assuming that increasing the current changes the direction of the magnetic field; correction: increasing the current increases the field strength, while reversing the current reverses the field direction.