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1998 - WAEC Physics Past Questions and Answers - page 5

41

Calculate the resistance of the filament of lamp rated at 240V 60W

A
240\(\Omega\)
B
360\(\Omega\)
C
960\(\Omega\)
D
144\(\Omega\)
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42

The diagram above illustrates a freely suspended bar magnet NS hanging from a point in a horizontal ceiling. The thread used for suspending the magnet and the axis of the magnet are as indicated on the diagram. The angle marked (\theta) is called the angle os

A
depression
B
declination
C
variation
D
elevation
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43

Lenz's law of electromagnet states that

A
the induced charge is constant for a fixed change of force
B
a force is exerted on a current-carrying conductor in a magnetic field
C
the magnitude of the induced e.m.f in a circuit is proportional to the rate of change of the number of lines of force linking the circuit
D
the induced current in a conductor is in such a direction as to oppose the change producing it
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44

A proton of charge 1.6 x 1019C is projected into a uniform magnetic field of flux density with a constant speed of 1.6 x 106ms-1, calculate the magnitude of the force exerted on it by the field

A
0.0N
B
2.0 x 10-21N
C
1.3 x 10-17N
D
5.1 x 10-14N
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45

The direction of the magnetic field at a point in the vicinity of a bar magnetic is

A
along the line joining the point to the neutral point
B
always away from the south pole of the magnet
C
opposite the direction of theresultant field at that point
D
always towards the north pole of the magnet
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46

The diagram below illustrates an a.c.source of 50V(r.m.s.), (\frac{100}{\pi})Hz connected in series with an inductor of inductor of inductance L and a resistor of resistance R. The current in the circuit is 2A and the p.d across L and R are 30V and 40V respectively. Calculate the power factor of the circuit

A
1.33
B
1.25
C
0.80
D
0.75
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47

The diagram below illustrates an a.c.source of 50V(r.m.s.), (\frac{100}{\pi})Hz connected in series with an inductor of inductor of inductance L and a resistor of resistance R. The current in the circuit is 2A and the p.d across L and R are 30V and 40V respectively. Calculate the average power dissipated in the circuit

A
100W
B
80W
C
60W
D
20W
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48

Use the following data to determine the length L of a wire when a fore of 30N is applied, assuming Hooke's law is obeyed
(\begin{array}{c|c}\text{Force applied/N} & 0 & 5 & 10 & 30\ \hline \text{length of wire/mm} & 500.0 & 500.0 & 501.0 & L \end{array})

A
3.0mm
B
3.5mm
C
503.00mm
D
503.5mm
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49

Which of the following explains the concave meniscus of water in a clean glass tube? the

A
adhension between water and glass molecules is greater than the sdhension between water molecules
B
cohension between water molecules is greater then the adhension between glass and water molecule
C
molecules of water near the glass move faster than the molecules at the centre of the tube
D
molecules of water at the water-air boundary are often attracted to the centre of the tube
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50

An electron is accelerated from rest through a potential difference of 70kV in a vacuum. Calculate the maximum speed acquired by the electron (electronic charge = -1.6 x 10-19; mass of an electron = 9.1 x 10-31kg)

A
3.00 x 108ms-1
B
2.46 x 108ms-1
C
1.57 x 108ms-1
D
1.32 x 108ms-1
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