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WAEC Physics Past Questions & Answers - Page 14

66.

Which of the following statements about electric potential energy is not correct?

A.

The electric potential energy of a positively charged particle increases when it moves to a point of higher potential

B.

The electric potential energy of a negatively charged particle increases when it moves to a point of lower potential

C.

The electric potential energy of a positively charged particle decreases when it moves to a point of higher potential

D.

The work done in taking a charged particle around a closed path in an electric field is zero.

Correct answer is B

The potential energy for a positive charge increases when it moves against an electric field

And decreases when it moves with the electric field;

The opposite is true for a negative charge. Unless the unit charge crosses a changing magnetic field, its potential at any given point does not depend on the path taken.

67.

Three cells each of emf, 1.0 V, and internal resistance, 2 Ω, are connected in parallel across a 3Ω  resistor. Determine the current in the resistor.

A.

0.90A

B.

0.39A

C.

0.30A

D.

0.01A

Correct answer is C

Given Data: Emf = 1v, r = 2 ohms, R = 3 ohms, I = ?

3 resistance in parallel = 1r1 + 1r21r3

1rT121212

1rT1+1+12

1rT32

cross multiply

rT23 or 0.67

E = I(R+r) 

1 = I(3+0.67)

1 = I(3.67)

1 ÷ 3.67 = I

0.27 = I

: I ≈ 0.30A

68.

Which of the following statements about a straight current-carrying wire placed in a uniform magnetic field is correct? The wire experiences ---------------

A.

maximum motor force if the current reverses its direction

B.

no motor force of it is parallel to the field

C.

no motor force if it is perpendicular to the field

D.

a motor force with constant direction if either the current or the magnetic field is reversed

Correct answer is B

The greatest force is experienced when the conductor is at right angle to the field.

I.e at perpendicular or Ø = 90°

69.

A body of mass, M, moving with velocity, V, has a wavelength, X, associated with it. This phenomenon is called----------

A.

photoelectric effect

B.

heisenberg's uncertainty principle

C.

compton effect

D.

wave-particles paradox

Correct answer is A

The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material

70.

The magnetic material produced from the chemical combination of metal oxides and has a very high resistance to electric current is called

A.

ferrite substance

B.

paramagnetic substance

C.

ferromagnetic substance

D.

diamagnetic substance

Correct answer is A

Ferrite magnets are non-conductive aferromagnetic ceramic compounds derived from iron oxides such as Haematite (Fe203) or Magnetite (Fe304) and other metal oxides such as Barium and Strontium.

Ferrite is a polycrystal, sintered material with high electrical resistivity. The high resistance of ferrite makes eddy current losses extremely low at high frequencies.