Grade 10 electricity – Magnetism Quiz
1. What are the two ends of a bar magnet called?
A bar magnet has two poles called the north and south poles where the magnetic effect is strongest.
2. Which material is most strongly attracted to a magnet and commonly used as cores in electromagnets?
Soft iron is easily magnetised and demagnetised, making it ideal for electromagnet cores to increase magnetic strength.
3. What is the shape of magnetic field lines around a bar magnet?
Magnetic field lines form closed loops leaving the north pole and entering the south pole, showing direction and continuity of the field.
4. A compass needle points towards the Earth's magnetic north because the needle itself is a small magnet. Which pole of the needle points toward Earth's geographic north?
The Earth's magnetic pole near geographic north is actually a magnetic south pole; so the needle's south-seeking pole points toward geographic north.
5. What did Hans Christian Ørsted discover about electricity and magnetism?
Ørsted found that an electric current in a wire creates a magnetic field around the wire, linking electricity and magnetism.
6. Which rule helps determine the direction of the magnetic field around a straight current-carrying conductor?
Using the right-hand rule (thumb along current, fingers curl) shows the circular direction of the magnetic field around a straight conductor.
7. Which factor does NOT increase the strength of an electromagnet?
Plastic is non-magnetic and does not concentrate magnetic field lines, so it does not strengthen an electromagnet; the others do.
8. What is a solenoid?
A solenoid is a helical coil of wire; when current passes through it, it produces a magnetic field similar to that of a bar magnet inside the coil.
9. Which of the following is a characteristic of magnetic field lines?
Magnetic field lines never cross because at any point in space the magnetic field has a single direction.
10. Which materials are strongly magnetic and commonly used to make permanent magnets?
Iron, nickel and cobalt are ferromagnetic materials that can be strongly magnetised and are used for permanent magnets.
11. What happens to the magnetic domains of a piece of soft iron when it is placed in a magnetic field?
Magnetic domains in soft iron line up with the external field, causing the material to become magnetised.
12. In a simple electric motor, what causes the coil to rotate?
A current in the motor's coil experiences a magnetic force (Lorentz force) that produces torque and causes rotation.
13. Which law explains the induced emf in a coil when the magnetic flux through it changes?
Faraday's law states that a changing magnetic flux induces an emf in a coil; this is the basis for generators and transformers.
14. What is the SI unit of magnetic flux density (magnetic field strength)?
The SI unit of magnetic flux density is the tesla (T), which measures the strength of a magnetic field.
15. Which device uses electromagnetism to convert electrical energy into mechanical energy?
An electric motor uses magnetic forces on current-carrying conductors to produce mechanical rotation from electrical energy.
16. What is a magnetic field?
A magnetic field is the space around magnets or currents in which magnetic forces can be detected and can influence other magnetic materials or currents.
17. Which statement about magnetic poles is correct?
Magnetic poles behave such that similar poles (north-north or south-south) repel, and opposite poles (north-south) attract.
18. What happens when you cut a bar magnet into two pieces?
When a magnet is cut, magnetic domains in each piece still form north and south poles, so both pieces are magnets.
19. How can you demagnetise a soft iron core used in an electromagnet easily?
Soft iron loses its induced magnetism quickly when the external magnetising current is removed and domains return to random orientations.
20. Which of the following best describes a permanent magnet?
Permanent magnets (like steel) keep their magnetic properties without needing an external magnetic field or current.
21. In Fleming's left-hand rule for motors, what does the middle finger represent?
In Fleming's left-hand rule: thumb = motion (force), first finger = magnetic field, middle finger = current. It helps find force direction in motors.
22. Which effect demonstrates that a changing magnetic field can produce an electric current?
Electromagnetic induction is the process where a changing magnetic flux induces an emf and can produce current in a conductor.
23. A coil moves into a magnetic field and an induced current is observed. What will happen to the coil's motion if it is free to move?
Lenz's law states induced currents produce magnetic effects that oppose the change in flux, causing a resisting force that slows the motion.
24. Which instrument measures the direction and relative strength of magnetic fields and is commonly used in schools?
A compass needle aligns with the local magnetic field, showing its direction and giving a simple indication of field strength by needle stability.
25. Why are iron nails placed inside the coil of an electromagnet in devices like cranes for scrap yards?
Placing an iron core in a coil increases the magnetic flux and strengthens the electromagnet, allowing it to lift heavier metal objects.
26. Which of these will increase the magnetic flux through a coil?
Magnetic flux through the coil changes more quickly if the magnet is moved faster, leading to a larger induced emf according to Faraday's law.