برقی مقناطیسیت

Written by Dr. Hamza Farooq (Physics)

دسویں جماعت · طبیعیات · 9 سوالات

نام: ____________________ تاریخ: ____________

A current carrying wire is surrounded by:
- A A gravitational field only
- B A magnetic field
- C Nothing
- D A sound field
A device that converts mechanical energy into electrical energy is a:
- A Battery
- B Transformer
- C Motor
- D Generator
A transformer works on the principle of:
- A Reflection
- B Mutual induction
- C Friction
- D Refraction
A step up transformer has:
- A More turns in the primary
- B More turns in the secondary
- C No core
- D Equal turns
A transformer has 100 primary turns, 500 secondary turns and a 20 V input. What is the output voltage?
- A 100 V
- B 20 V
- C 500 V
- D 4 V
The magnetic field lines outside a bar magnet go from the:
- A South pole to the north pole
- B Centre to the south pole
- C North pole to the south pole
- D Centre to the north pole
A coil in a magnetic field carrying current experiences:
- A A sound
- B A cooling effect
- C No force
- D A turning force
An electric motor changes:
- A Mechanical into electrical
- B Heat into light
- C Sound into light
- D Electrical energy into mechanical energy
The core of a transformer is made of soft iron because it:
- A Is easily magnetised and demagnetised
- B Is a poor conductor
- C Is cheap only
- D Is lighter

جوابی کلید

1. B, 2. D, 3. B, 4. B, 5. A, 6. C, 7. D, 8. D, 9. A

Oersted showed that a current produces a magnetic field around the wire.
A generator turns mechanical energy into electrical energy.
Changing current in the primary induces a voltage in the secondary: mutual induction.
More turns in the secondary give a higher output voltage.
Vs = Vp x Ns / Np = 20 x 500 / 100 = 100 V.
Field lines leave the north pole.
This is the basis of the electric motor.
It uses current in a field to produce motion.
Soft iron concentrates the changing flux.