Starter quiz
- In a drawing of the magnetic field lines around a magnet, the field lines are closer together in some areas than others. Which of the following statements is correct?
- The closeness of the field lines does not mean anything.
- The magnetic field is stronger where the field lines are closer together. ✓
- The magnetic field is weaker where the field lines are closer together.
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- What do the directions of magnetic field lines represent?
- The positions of a north-facing pole.
- The positions of a south-facing pole.
- The directions of the forces on a north-facing pole. ✓
- The directions of the forces on a south-facing pole.
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- A compass usually points north. If the needle of a compass is deflected (changes direction) so that it no longer points north, which of the following are possible explanations?
- It is near a piece of copper.
- It is near a wire that is carrying a current. ✓
- It is near the north-seeking end of a bar magnet. ✓
- It is near the south-seeking end of a bar magnet. ✓
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- Which of the following statements are correct?
- Magnetic field line arrows point towards a north-seeking pole.
- Magnetic field line arrows point towards a south-seeking pole. ✓
- Current flows from the positive terminal to the negative terminal of a battery. ✓
- Current flows from the negative terminal to the positive terminal of a battery.
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- Two variables have this relationship: whenever the value of one variable is multiplied by a number, the value of the other variable is multiplied by the same number. The two variables are directly...
- rational.
- relational.
- positional.
- proportional. ✓
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Two equal and opposite forces act on the ends of a ruler as shown by the arrows. The ruler is initially stationary. Which of the following describes what happens to the ruler?- It does not move.
- It moves to the left.
- It moves to the right.
- It rotates clockwise.
- It rotates anticlockwise. ✓
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Exit quiz
- Which of the following statements about magnetic flux density are correct?
- Its symbol is and its unit is T. ✓
- Its symbol is and its unit is B.
- It is always greater if the magnet is larger.
- It is always greater if the magnetic field is stronger. ✓
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- Which of the following describes the magnetic field lines near a straight current-carrying wire?
- They are circular, with their centres on the wire. ✓
- They have the same shape as the field lines around a bar magnet.
- They are straight and point in the same direction as the current.
- They are straight and point in the opposite direction to the current.
- There are no magnetic field lines.
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- Which of the following are characteristics of a uniform magnetic field?
- Its field lines are evenly spaced. ✓
- It has the same strength everywhere. ✓
- Its field lines are perpendicular to each other.
- The arrows on its field lines all point in the same direction. ✓
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- Fleming’s left-hand rule can be used to predict the direction of the force on a current-carrying wire in a magnetic field. Match each digit with what it represents in the left-hand rule.
- first finger⇔represents the magnetic field direction ✓
- second finger⇔represents the direction of the current in the wire ✓
- third finger⇔is not used in Fleming’s left-hand rule ✓
- thumb⇔represents the direction of the force on the wire ✓
- A 12 cm length of straight wire carrying a current of 1.2 A is in a uniform magnetic field with flux density 0.50 T. The size of the force on the wire is ______ N.
- '0.072' ✓
The diagram shows a current-carrying loop of wire in a uniform magnetic field. Three sides of the loop are labelled P, Q and R. Match each side to a description of the force acting on it.- side P⇔An upwards force acts. ✓
- side Q⇔No force acts. ✓
- side R⇔A downwards force acts. ✓
Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- The magnetic field lines around a current-carrying wire are concentric circles
- In a uniform magnetic field, a current carrying wire is forced in one direction
- Fleming’s left–hand rule can be used to predict the direction of movement of a current–carrying wire in a magnetic field
- The force on a current–carrying conductor at right angles to a magnetic field, F, is found using F = B I l.
- Opposite sides of a conducting coil in a uniform magnetic field are forced to move in opposite directions
Common misconception
It is not clear how the magnetic field around a conducting wire interacts with a uniform magnetic field.
Focus on observing and predicting the direction that a conducting wire is forced in by a uniform magnetic field, and openly admit that explaining this in terms of how the magnetic field interact is too challenging to include in the syllabus.
Keywords
Uniform magnetic field - has evenly spaced field lines and the strength of the magnetic field is the same everywhere
Fleming’s left-hand rule - indicates the direction a conducting wire is forced to move in a uniform magnetic field
Magnetic flux density, b - is a measure of the strength of a magnetic field
Tesla (t) - is the unit that magnetic flux density is measured in
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