EXCEL IRISH PART

State which of the following is false. The capacitance of a capacitor

• is proportional to the cross-sectional area of the plates
• is proportional to the distance between the plates
• depends on the number of plates
• is proportional to the relative permittivity of the dielectric

Magnetic flux can always be attributed to:

• A. Ferromagnetic materials
• B. Aligned atoms
• C. Motion of charged particles
• D. The geomagnetic field

A straight conductor 500 mm long is moved with constant velocity at right angles both to its length and to a uniform magnetic field. Given that the e.m.f. induced in the conductor is 2.5 V and the velocity is 5 m/s, calculate the flux density of the magnetic field. If the conductor forms part of a closed circuit of total resistance 5 ohms, calculate the force on the conductor.

• A. 0.25 N
• B. 0.025 N
• C. 2.5 N
• D. 250 N

Which of the following statements is true?

• A. Unlike charges repel each other.
• B. Like charges repel each other.
• C. Unlike charges attract each other
• D. Both B and C.

A changing magnetic field:

• A. Produces an electric current in an insulator.
• B. Magnetizes the earth.
• C. Produces a fluctuating electric field.
• Results from a steady electric current.

A conductor of length 15 cm is moved at 750 mm/s at right-angles to a uniform flux density of 1.2 T. Determine the e.m.f. induced in the conductor.

• A. 0.135 V
• B. 1.350 V
• C. 0.0135 V
• D. 13.50 V

For the current carrying conductor lying in the magnetic field shown in the figure below, the direction of the force on the conductor is:

• A. downwards
• B. to the right
• C. upwards
• D. to the left

Which is the wrong statement? The magnetizing force at the center of a circular coil varies

• A. directly as the number of its turns
• B. directly as the current
• C. directly as its radius
• D. inversely as its radius

A 25 cm long conductor moves at a uniform speed of 8 m/s through a uniform magnetic field of flux density 1.2 T. Determine the current flowing in the conductor when its ends are connected to a load of 15 ohms resistance.

• A. 1.6 A
• B. 0.16 A
• C. 16 A
• D. 0.016 A

Two bar magnets are placed parallel to each other and about 2 cm apart, such that the south pole of one magnet is adjacent to the north pole of the other. With this arrangement, the magnets will:

• A. attract each other
• B. have no effect on each other
• C. repel each other
• D. lose their magnetism