Electromagnetism is the branch of physics that studies the relationship between electricity and magnetism. This chapter covers magnetic effects of current, electromagnets, electromagnetic induction, and applications like electric bells, motors, and generators. It also explains Faraday’s laws, Fleming’s rules, and the working principles of transformers and power generation.
1. Which scientist discovered the magnetic effect of electric current?
- A. Oersted ✅
- B. Faraday
- C. Ampere
- D. Maxwell
Explanation: In 1820, Oersted discovered that a current-carrying conductor produces a magnetic field around it.
2. The right-hand grip rule is used to find:
- A. Direction of magnetic field around a current-carrying wire ✅
- B. Direction of current in a generator
- C. Direction of force on a conductor
- D. Direction of electric field
Explanation: The right-hand grip rule relates the thumb to current direction and fingers to magnetic field direction.
3. Electromagnets are made by:
- A. Passing current through a coil wound around a soft iron core ✅
- B. Using a permanent magnet
- C. Using copper plates
- D. Charging a capacitor
Explanation: Soft iron enhances the magnetic field when current flows through the surrounding coil.
4. Faraday’s first law of electromagnetic induction states that:
- A. A changing magnetic field induces an emf ✅
- B. Current produces a magnetic field
- C. Magnetic poles exist in pairs
- D. Electric charge is conserved
Explanation: Faraday found that a changing magnetic flux through a circuit induces an electromotive force (emf).
5. Fleming’s left-hand rule is used to find:
- A. Direction of force on a current-carrying conductor in a magnetic field ✅
- B. Direction of induced current
- C. Magnetic polarity
- D. Electric potential
Explanation: Fleming’s left-hand rule relates the directions of current, magnetic field, and force.
6. Fleming’s right-hand rule is applied to:
- A. Find direction of induced current ✅
- B. Find direction of force
- C. Find magnetic field direction
- D. Find electric potential
Explanation: The right-hand rule is used for generators to find induced current direction.
7. The working principle of an electric motor is based on:
- A. Force on a current-carrying conductor in a magnetic field ✅
- B. Induction of emf
- C. Electrostatics
- D. Heating effect of current
Explanation: Motors convert electrical energy into mechanical energy using this principle.
8. The device used to convert mechanical energy into electrical energy is:
- A. Generator ✅
- B. Motor
- C. Transformer
- D. Electromagnet
Explanation: Generators use electromagnetic induction to produce electricity from mechanical rotation.
9. Which core material is preferred for transformers?
- A. Soft iron ✅
- B. Steel
- C. Copper
- D. Aluminium
Explanation: Soft iron has high magnetic permeability and low hysteresis loss, ideal for transformers.
10. Step-up transformers increase:
- A. Voltage ✅
- B. Current
- C. Resistance
- D. Power
Explanation: Step-up transformers increase voltage while decreasing current.
11. The SI unit of magnetic flux is:
- A. Weber ✅
- B. Tesla
- C. Henry
- D. Gauss
Explanation: Magnetic flux is measured in webers (Wb).
12. Which rule determines the polarity of an electromagnet?
- A. Right-hand grip rule ✅
- B. Fleming’s left-hand rule
- C. Maxwell’s rule
- D. Ampere’s rule
Explanation: The right-hand grip rule helps find the north and south poles of an electromagnet.
13. Which effect of current is used in electric bells?
- A. Magnetic effect ✅
- B. Heating effect
- C. Chemical effect
- D. Optical effect
Explanation: Electric bells work by attracting a metal striker using an electromagnet.
14. Faraday’s second law states that induced emf is proportional to:
- A. Rate of change of magnetic flux ✅
- B. Magnetic pole strength
- C. Number of field lines
- D. Direction of field
Explanation: The faster the magnetic flux changes, the greater the induced emf.
15. Which device changes AC voltage levels?
- A. Transformer ✅
- B. Generator
- C. Motor
- D. Rectifier
Explanation: Transformers step voltage up or down using electromagnetic induction.