Electromagnetic Induction

A bar magnet falling through a loop with the north pole facing down induces a current

• in a clockwise direction

• in an anticlockwise direction

• first in a clockwise, then in an anticlockwise direction

• first in an anticlockwise, then in a clockwise direction

Coil B lies in the same plane as coil A. If the switch is closed which direction will current flow in coil B?

• Clockwise

• Anticlockwise

• No current will flow

• A current will only flow if coil B is turned perpendicular to coil A

Magnetic flux density has the units:

• Wb m^–2

• Wb A^–1 m^–1

• T m^–1

• T m

A uniform magnetic field threads a circular loop with area A at angle  $\theta$ . The strength of the field is increasing at a uniform rate R. What equation describes the EMF induced in the loop?

•  $BA\cos\theta$  

•  $RA\sin\theta$  

•  $BIL\sin\theta$  

•  $RA\cos\theta$  

An ideal transformer has n_p primary turns, and n_s secondary turns. The voltage across the primary is V_p. Determine the induced in the secondary, V_s.

• $\frac{n_p}{n_s}V_p$

• $\frac{n_s}{n_p}V_p$

• $\frac{n_s}{V_{p\ }}n_p$

• $n_pn_sV_p$

A transformer designed to step-down 240 V mains voltage to a voltage of 6 V AC. Calculate the number of turns on the secondary coil, given that the primary coil has 2000 turns.

• 20 turns

• 50 turns

• 150 turns

• 200 turns

A 200-turn coil with area 50 cm² is placed perpendicular to a magnetic field as shown in the figure. The intensity of the field varies from 30 mT to 10 mT in a time of 0.02 s. Calculate the voltage on the coil.

• 0.1 V

• 1 V

• 100 V

• 10⁷ V

Determine the direction of motion of the magnet when the current flows as shown.

• towards the solenoid

• away from the solenoid 

• standing still

• moving back and forth

Determine the EMF induced in a coil that has 1200 evenly spaced turns and a radius of 2.5 cm, when a magnet is brought near its end so that the magnetic field inside it is increased from 0 to 0.060 T in 20 ms.

• 0.0032 V

• 1.52 V

• 7.06 V

• 9.86 V

An aircraft is flying through Earth’s magnetic field at a steady horizontal speed of 800 km/h. The vertical component of Earth’s magnetic field is 5.0 × 10^–5 T. Determine the EMF generated between the wing tips if they are 25 m apart.

• 0.0

• 0.28 V

• 1 V

• 22.8 V