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WAEC Physics Past Questions & Answers - Page 43

211.

An electron of mass 9.1 x 1031 kg moves with a speed of 2.0 x 106 ms1 round the nucleus of an atom in a Circular path of radius

6.1 x 1011 m. Calculate the centripetal force acting on the electron.
 

A.

7.7 x 1047 N

B.

6.0 x 108N

C.

3.0 x 1014N

D.

1.3 x 1026N

Correct answer is B

Centripetal force (Fr) = MV2r 

i.e. Fr = Mv2r 

= 9.1×1031×2.0×106×2.0×1066.1×1011

= (36.4×10196.1×1011) N

= 5.967 x 108

~ 6.0 x 108 N

 

212.

An electron of mass 9.1 x 1031 kg moves with a speed of 2.0 x 106 ms1 round the nucleus of an atom in a Circular path of radius 6.1 x 10(^{11}\) m. Determine the angular speed of the electron.

A.

3.28 x 1016 rad s1

B.

8.55 x 103 rad s1

C.

9.11 x 1013 rad s1

D.

5.22 x 1015 rad s1

Correct answer is A

Angular speed of the electron (W) 

w = VelocityRadius=VR

= 2.0×1066.1×1011 

= 3.28 x 1016 rads1

213.

Which of the following devices is used for storing electric charges?

A.

Transformer

B.

Ammeter

C.

Potentiometer

D.

Capacitor

Correct answer is D

No explanation has been provided for this answer.

214.

The diagram above illustrates a meter bridge circuit underbalanced conditions. Determine the value of x.

A.

50.cm

B.

10.0 cm

C.

28.6 cm

D.

57.2 cm

Correct answer is A

Using wheatstone bridge principle;

2x=2(100x)

2(100 - x) = 2 x x

200 = 2x+2x 

200 = 4x

x = 2004

= 50cm 

215.

Which of the following statements is the correct reason for using soft iron in making the armature or an electric bell?

A.

It is a diamagnetic material

B.

It loses its magnetism readily

C.

It is not easily magnetized

D.

It retains its magnetism for a long time

Correct answer is B

No explanation has been provided for this answer.