2018 - JAMB Physics Past Questions and Answers - page 6

51

The energy needed to move a unit positive charge around a complete electric circuit is called the

A
electromotive force
B
electric potential difference
C
electric energy
D
kinetic energy
correct option: a

Electric potential difference is the work needed per unit of charge to move a test charge between the two points.

Electric energy is the energy derived from electric potential energy.

In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes.

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52

A force of 5N acts at a point Y on a rod XYZ as shown in this diagram. If XYZ is 2m, what is the moment of the force about point X?

A
0Nm
B
3Nm
C
7Nm
D
10Nm
correct option: d

Moment = Force × Distance
= 5N x 2m
= 10Nm

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53

The resistance of a 40W car head lamp, drawing current from a 12V battery is ____.

A
0.3Ω
B
3.3Ω
C
3.6Ω
D
4.8Ω
correct option: c

Power delivered to head lamp = \(\frac{V_2}{R}\)

  = 40W

  R = \(\frac{V_2}{40}\)

  = \(\frac{(12 × 2)}{40}\)

  = 3.6Ω

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54

A beam of light is incident from air to water at an angle of 300. Find the angle of refraction if the refractive index of water is 4/3

A
15\(^o\)
B
18\(^o\)
C
22\(^o\)
D
24\(^o\)
correct option: c

X = \(\frac{4}{3}\) r = ?

  Shell’s law:. 7 = \(\frac{Sin 2^0}{ Sin r^0}\)

  \(\frac{V}{g}\) = \(\frac{Sin 30^0}{Sin r^0}\)

  Sin\(r^0\) = \(\frac{3 Sin 30^0}{4}\)

  Sin \(r^0\) = 0.375

  R \(^o\) = Sin-1 (0.375)

  R \(^o\) = 22.02 \(^o\)

  R \(^o\) = 22 \(^o\)

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55

An electric heating coil rated at 1Kw is used to heat 2kg of water for 2 minutes. The initial water temperature is 30\(^o\)C. Taking the specific heat of the water as 4,000Jkg \(^{-1}\) and neglecting that of the container, the final water temperature is

A
15.0\(^o\)C
B
45.0\(^o\)C
C
52.5\(^o\)C
D
C. 60.0\(^o\)C
correct option: c

Power, P = 1kw=100W

  Time, t = 2mins = 2 × 60 = 120secs

  Energy = P×t

  1000 × 120 = 120,000J

  Energy = mc(θ\(_2\) – θ\(_1\))

  120,000 = 2 × 4000(θ\(_2\) – θ\(_1\))

  θ2 = 30 + 15 = 45 \(^o\) C

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56

What flows to the earth by connecting the conductor to the earth?

A
Electrons
B
Ion
C
Neutron
D
Proton
correct option: a

Ion is an atom with a net electric charge due to loss or gain of one or more electrons
Neutron is a subatomic particle of about the same mass as a proton without electric charge.
Proton is a subatomic particle with a positive charge

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57

Temperature is the property of a body which is proportional to the ____.

A
total kinetic energy of its molecules
B
average kinetic energy of its molecules
C
average speed of its molecules
D
maximum speed of its molecules
correct option: b
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58

The product of force and time is?

A
Impulse
B
Momentum
C
Inertia
D
Friction
correct option: a

An impulse is a measure of the net force on the object multiplied by the time period over which this force is applied. Mathematically, impulse, F = ma.

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59

Which of the following concepts is not an evidence of the particles nature of matter?

A
Diffusion
B
Brownian motion
C
Diffraction
D
Crystallization
correct option: d

Diffusion: the net movement of molecules/atoms from a region of high concentration to low concentration.

  Brownian motion: the erratic random movement of microscopic particles in a field.

 While diffraction is the various phenomena that occur when a wave encounters an obstacle.

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60

A car traveled at a uniform speed of 100km/h, spends 15m moving from point A to point B along its route. The distance between A and B is

A
50km
B
25km
C
15km
D
10km
correct option: b

Distance, d = speed × time

  = \(\frac{(\frac{100 \times 103}{3600})}{15 \times 60}\)

  = 25km

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