1

If 16mA of current flows through a conductor in one second, the number of electron transported per seconds is

[1 electronic charge = 1.6 x 10^{-19}C]

[1 electronic charge = 1.6 x 10

A

1.00 x 10^{20}

B

2.56 x 10^{-18}

C

2.56 x ^{-17}

D

1.00 x 10^{17}

CORRECT OPTION:
d

Current (I) = ^{q}/_{t} → q = i x t

= 16 x 10^{-3} x 1

= 1.6 x 10^{-2}C

But 1.6 x 10^{-19}C = I electronic charge

1 coulomb = 1 / (1.6x10^{-19})

∴ 1.6 x 10^{-2} coulombs = 1 / (1.6x10^{-19}) x 1.6x10^{-2} / 1

= 1.0 x 10^{-2} x 10^{19}

= 1.0 x 10^{17}

= 16 x 10

= 1.6 x 10

But 1.6 x 10

1 coulomb = 1 / (1.6x10

∴ 1.6 x 10

= 1.0 x 10

= 1.0 x 10

2

Electrical appliances at home are normally earthed so that

A

the appliances are maintained at a lower p.d than the earth

B

both the a.c and d.c sources can be used

C

a person touching the appliances is safe from electric shock

D

the appliances are maintained at a higher p.d than the earth

CORRECT OPTION:
c

3

Given three capacitors 0.3μF, 0.5μF and 0.2μF, the joint capacitance when arranged to give minimum capacitance is

A

0.1μF

B

0.3μF

C

1.0μF

D

0.5μF

CORRECT OPTION:
a

=> C = 1 / 10.3333 = 0.09677

≅ 0.1μF

∴ C = 0.1μF

4

The difference between X-rays and gamma rays is that

A

x-rays are more penetrating than gamma rays

B

x-rays are electromagnetic radiations while gamma rays are negatively charged radiation

C

x-rays have higher frequencies than gamma rays

D

x-rays arise from energy changes in the electronic structure of atoms while gamma rays come from the nucleus

CORRECT OPTION:
d

5

To protect a material from the influnce of an external magnetic field, the materials should be kept

A

square steel ring

B

triangular zinc ring

C

soft iron ring

D

loop of copper wire

CORRECT OPTION:
c

In order to protect a material from the influence of an external magnetic field, the material is placed in a soft iron ring, usually referred to as magnetic screening.

6

In the diagram above, the ratio of he electric power dissipated in the 6Ω and the 3Ω resistor respectively is

A

2:1

B

2:2

C

1:3

D

1:2

CORRECT OPTION:
d

Power, P = I^{2}R;

and I =^{E}/_{R}

But effective Parallel resistance: is given by:

^{1}/_{R} = ^{1}/_{6} + ^{1}/_{3} = ^{1+2}/_{6} = ^{3}/_{6} => R = ^{6}/_{3} = 2Ω

Current I =^{E}/_{R} = ^{12}/_{2} = 6A

But I_{1} = (^{R1}/_{R1+R2}) x 1 = ^{3}/_{9} x 6 = 2A

again I_{1} = (^{R1}/_{R1+R2}) x 1 = ^{6}/_{9} x 6 = 4A

∴P_{1} = I_{1}^{2} R_{1} = 2 x 2 x 6 = 24W

P_{2} = I_{2}^{2} R_{2} = 4 x 4 x 3 = 48W

thus^{P1}/_{P2} = ^{24}/_{48} = ^{1}/_{2} ; OR P_{1} : P_{2} = 1:2

and I =

But effective Parallel resistance: is given by:

Current I =

But I

again I

∴P

P

thus

7

If the angle between two vector P and Q is O^{o}, the vectors are said to

A

intersect at the angle 45^{o}

B

intersect at the angle 60^{o}

C

be parallel

D

be perpendicular

CORRECT OPTION:
c

8

A body of mass 4kg is acted on by a constant force of 12N for 3 seconds. The kinetic energy gained by the body at the end of the time is

A

144J

B

162J

C

81J

D

72J

CORRECT OPTION:
b

K.E = ^{1}/_{2}MV^{2}

Force, F = ma => a =^{F}/_{m} = ^{12}/_{4} = 3ms^{-2}

But a = (V-U) / t => V = u + at

If the initial velocity U = 0, then V = at = 3 x 3 = 9ms^{-2}

∴ K.E, =^{1}/_{2}ms^{-2}

^{1}/_{2} 4 x 9 x 9 = 162J

Force, F = ma => a =

But a = (V-U) / t => V = u + at

If the initial velocity U = 0, then V = at = 3 x 3 = 9ms

∴ K.E, =

9

A machine whose efficiency is 60% has a velocity ratio of 5. If a force of 500N is applied to lift a load P, what is the magnitude of P?

A

1500N

B

500N

C

4166N

D

750N

CORRECT OPTION:
a

efficiency = (M.A / V.R) x 100/1 => ^{60}/_{100} = ^{M.A}/_{5}

∴M.A = (60 X 5) / 100 = 3

But M.A = Load/Effort; => 3 = Load/500

∴Load = 500 x 3

= 1500N

∴M.A = (60 X 5) / 100 = 3

But M.A = Load/Effort; => 3 = Load/500

∴Load = 500 x 3

= 1500N

10

II. Rocket propulsion

III. The recoil of a gun

IV. A person walking

Which of the above is based on Newton's third law of motion

A

I and II only

B

I, II, III, and IV only

C

I and III only

D

I, II and III only

CORRECT OPTION:
d

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