2019 - JAMB Physics Past Questions and Answers - page 2

11

Electrons were discovered by

A

Dalton

B

James Charwick

C

J.J. Thompson

D

Niels Bohr

correct option: c

J.J Thompson discovered electron in 1879

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12

Which of the following is/are the limitations to the Rutherford's atomic models?

I. It is applicable when energy is radiated as electrons are revolving

II. It is applicable when energy is radiated in a continuous mode

III. It is applicable to an atom with only one electron in the other shell

A

I only

B

II only

C

I & II only

D

I, II & III only

correct option: c

Rutherford's model assumed the following which forms limitations of the model:

  • energy is radiated when electrons are revolving
  • energy is radiated in a continuous mode
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13

Which of the following equations is the correct definition of the reactance of an indicator L?

A

Reactance = (Amplitude of voltage) \(\div\) (Amplitude of current)

B

Reactance = (Amplitude of voltage) x (Amplitude of current)

C

Reactance = (Amplitude of current)\(^2\) \(\div\) (Amplitude of voltage)

D

Reactance = (Amplitude of current)\(^2\) \(\div\) (Amplitude of voltage)\(\frac{1}{2}\)

correct option: a

Reactance is a form of opposition that electronic components exhibit to the passage of alternating current (alternating current) because of capacitance or inductance.

Resistance and reactance combine to form impedance

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14

Ripple in a power supply unit is caused by

A

using an alternating current source

B

forward voltage drop

C

heavy load

D

using a zener diode

correct option: d

The fluctuation of d.c signal results from the rectification of AC to DC

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15

When the temperature of a liquid is increased, its surface tension

A

increases

B

decreases

C

remain constant

D

increases then decreases

correct option: b

In general, surface tension decreases when the temperature increases because cohesive forces decrease with an increase of molecular thermal activity. The influence of the surrounding environment is due to the adhesive action of liquid molecules that they have at the interface.

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16

The distance between an object and its real image in a convex lens is 40cm. If the magnification of the image is 3, calculate the focal length of the lens

A

6.5 cm

B

7.5 cm

C

8.5 cm

D

4.5 cm

correct option: b

 

Formula:

u + v = 40

\(\frac{v}{u}\) = 3

v = 3u

u + 3u = 40

4u = 40

u = 10cm

v = 3u = 30cm

f = \(\frac{uv}{u + v} = \frac{10(30)}{10 + 30} = \frac{300}{40}\)

f = 7.5 cm

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17

A ray of light passes through the centre of curvature of a concave mirror and strikes the mirror. At what angle is the ray reflected?

A

180\(^o\)

B

90\(^o\)

C

0\(^o\)

D

60\(^o\)

correct option: c

When a ray of light passes through the centre of curvature, it is returned along the same path with the angle difference along the same path equal to zero

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18

The pin-hole camera produces a less sharply defined image when the

A

pin-hole is larger

B

illumination is less

C

screen is further from the pin-hole

D

object is further from the pin-hole

correct option: a

Increased brightness leads to a less sharp or blurred image. Also, increase brightness is consequent upon a large hole or multiple pinholes

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19

A straight wire 15cm long, carrying a current of 6.0A is in a uniform field of 0.40T. What is the force on the wire when it is at right angle to the field

A

0.46N

B

0.35N

C

0.36N

D

0,24N

correct option: c

F = BIL

F = 0.4 x 6 x \(\frac{15}{100}\)

F = 0.36N

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20

The pitch of a screw jack is 0.45cm and the arm is 60cm long. If the efficiency of the Jack is 75/π %, calculate the mechanical advantage.

A

400

B

300

C

200

D

150

correct option: c

P = 0.45cm,

L = 60cm,

Efficiency(eff) = 75/π%

VR Screw system = 2πr
P
= 2πL
P

 

M.A = Eff% × VR
100
= 75
π
× 1
100
× 2π × 60
0.45
= 75 × 800
300
= 200

Hence, M.A = 200

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