# 2004 - JAMB Physics Past Questions and Answers - page 1

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

[1 electronic charge = 1.6 x 10

^{-19}C]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) =

= 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

Users' Answers & Comments^{q}/_{t}→ q = i x t= 16 x 10

^{-3}x 1= 1.6 x 10

^{-2}CBut 1.6 x 10

^{-19}C = I electronic charge1 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}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

^{1}/

_{C}=

^{1}/

_{0.3}+

^{1}/

_{0.5}+

^{1}/

_{0.2}= 10.3333

=> 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.

Users' Answers & Comments6

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

and I =

But effective Parallel resistance: is given by:

Current I =

But I

again I

∴P

P

thus

Users' Answers & Comments^{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}= 2ΩCurrent I =

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

_{1}= (^{R1}/_{R1+R2}) x 1 =^{3}/_{9}x 6 = 2Aagain I

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

_{1}= I_{1}^{2}R_{1}= 2 x 2 x 6 = 24WP

_{2}= I_{2}^{2}R_{2}= 4 x 4 x 3 = 48Wthus

^{P1}/_{P2}=^{24}/_{48}=^{1}/_{2}; OR P_{1}: P_{2}= 1:27

If the angle between two vector P and Q is O

^{o}, the vectors are said toA

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 =

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, =

Users' Answers & Comments^{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 = 162J9

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 =>

∴M.A = (60 X 5) / 100 = 3

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

∴Load = 500 x 3

= 1500N

Users' Answers & Comments^{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

10

**I. Jet propelled aircraft**

II. Rocket propulsion

III. The recoil of a gun

IV. A person walking

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