2002 - JAMB Physics Past Questions and Answers - page 4
31
The eye controls the amount of light reaching the retina by adjusting the
A
cornea
B
iris
C
retina
D
optic nerve
correct option: b
The iris controls the amount of light by limiting the volume of light admitted. The lens then focuses the light onto the retina, forming an inverted image. The lens changes its shape to adjust the focus on both distant and near objects, a process called accommodation.
This adjustment is done by two sets of muscles in the iris
Users' Answers & CommentsThis adjustment is done by two sets of muscles in the iris
32
An electric iron is rated 1000W, 230V. What is the resistance of its elements?
A
51.9Ω
B
52.9Ω
C
55.9Ω
D
57.6Ω
correct option: b
Electric Power = IV = I2R = V2/R thus for a device rated 1000 W, 230V, from the relation P = V2/R, 1000 = (230)2/R
=> R = (230)2/1000
= 52900/1000 = 52.9Ω
Users' Answers & Comments=> R = (230)2/1000
= 52900/1000 = 52.9Ω
33
A
Both X and Y are negative
B
Both X and Y are positive
C
X is positive and Y is negative
D
X is negative and Y is positive
correct option: b
Users' Answers & Comments34
The electromagnetic wave that can produce a heating effect on the environment is
A
x -rays
B
ultraviolet rays
C
infrared rays
D
gamma rays
correct option: b
Users' Answers & Comments35
an electric cell with nominal voltage E has a resistance of 3Ω connected across it. If the voltage falls to 0.6E, the internal resistance of the cell is
A
1Ω
B
2Ω
C
3Ω
D
4Ω
correct option: c
I = V/R = 0.6E/3 = 0.2E
Again, I = E / (R+ϒ) = E / (3+ϒ)
Divide eqn (2) by eqn (1)
I/I = E / (3+ϒ) x I / 0.2E
=> 0.2(3+ϒ) = 1
0.6 x 0.2ϒ = 1
∴0.2ϒ = -0.6
=> ϒ = 0.6 / 0.2 = 3Ω
ϒ = 3Ω
Users' Answers & CommentsAgain, I = E / (R+ϒ) = E / (3+ϒ)
Divide eqn (2) by eqn (1)
I/I = E / (3+ϒ) x I / 0.2E
=> 0.2(3+ϒ) = 1
0.6 x 0.2ϒ = 1
∴0.2ϒ = -0.6
=> ϒ = 0.6 / 0.2 = 3Ω
ϒ = 3Ω
36
| 23 | Na + X → | 20 | F + | 4 | He | |
| 11 | 9 | 2 |
What particle is X in the reaction above?
A
Alpha
B
Beta
C
Neurons
D
Gamma
correct option: c
The particle in the reaction is neutron
Users' Answers & Comments| 23 | Na + | 1 | n → | 20 | F + | 4 | He |
| 11 | 0 | 9 | 2 |
37
Pure silicon can be converted to a p-type by adding a controlled amount of
A
trivalent atoms
B
tetravalent atoms
C
pentavalent atoms
D
hexavalent atoms
correct option: a
Users' Answers & Comments38
The energy associated with the photon of a radio transmission at 3 x 105 Hz is
[h = 6.63 x 10-34Js]
[h = 6.63 x 10-34Js]
A
2.00 x 10-28J
B
1.30 x 10-28J
C
2.00 x 10- 29J
D
1.30 x 10-29J
correct option: a
A photon of energy E = hf
= 6.63 x 10-34 x 3 x 105
= 19.89 x 10-29
= 2.0 x 10-28J
Users' Answers & Comments= 6.63 x 10-34 x 3 x 105
= 19.89 x 10-29
= 2.0 x 10-28J
39
The percentage of the original nuclei of the sample of a radioactive substance left after 5 half - lives is
A
8%
B
5%
C
3%
D
1%
correct option: c
After 5 half-lives, the fraction of any radio-active substance left = (1/2)5 = 1/32
Thus the percentage of the original nuclie = 1/32/1 x 100/1
assuming the original amount is unity percentage left
= 1/32 x 1400/1 = 3.12
Users' Answers & CommentsThus the percentage of the original nuclie = 1/32/1 x 100/1
assuming the original amount is unity percentage left
= 1/32 x 1400/1 = 3.12
40
From the generating station to each substation power is transmitted at a very high voltage so as to reduce
A
hysteresis loss
B
eddy current loss
C
magnetic flux leakage
D
heating in the cells
correct option: b
Users' Answers & Comments