2006 - JAMB Physics Past Questions and Answers - page 2
11
The main purpose of the transformer in an a.c radio set is to?
A
increase power to the radio
B
step up the voltage
C
convert energy from a.c to d.c
D
step down the voltage
correct option: d
Users' Answers & Comments12
An electric heater with a p.d of 240 V connected across its terminals has a total resistance of 960Ω. find the power rating of the heater.
A
0.25 W
B
4.00 W
C
38.40W
D
60.00W
correct option: d
Electrical power = IV or I2R or (V)/R
With V = 240v, R = 960Ω
Power (V2)/R = (240 X 240)/960
=60Watts
Users' Answers & CommentsWith V = 240v, R = 960Ω
Power (V2)/R = (240 X 240)/960
=60Watts
13
If the capacitance of an capacitor is C = (εA)/d, which of the following parameters is varied when a variable capacitors is used for tuning radio sets?
A
constant (ε) and area
B
area and distance.
C
constant (ε) only
D
distance only
correct option: b
Users' Answers & Comments14
When an a.c. voltage is applied to a capacitor, no power is consumed because the current
A
leads the voltage by 90°
B
lags behind the voltage by 90°
C
and voltage are in phase
D
and voltage are 180° out of phase
correct option: a
In a capacitive circuit, current leads voltage by 90°, or voltage lags current by 90°
Users' Answers & Comments15
The electrolyte in the Nickei-iron (Nife) accumulator is
A
potassium hydroxide solution
B
dilute tetraoxosulphate(VI)acid
C
copper tetraoxosulphate(VI)solution
D
ammonium chloride solution
correct option: a
Users' Answers & Comments16
During electrolysis, 2.0 g of a metal is deposited using a current of 0.5 A in 3 hours. The mass of the same metal which can be deposited using a current of 1.5 A in 1 hour is?
A
1.0 g
B
0.5 g
C
3.0 g
D
2.0 g
correct option: d
M = Itz; z = (M)/It = (2)/0.5 x 3 x 60 x 60
= 3.703 x 10-4 gc-1
∴ M = Itz = 1.5 x 1 x 60 x 60 x 3.703 x 10-4
= 1.99962g.
=2.0g
Users' Answers & Comments= 3.703 x 10-4 gc-1
∴ M = Itz = 1.5 x 1 x 60 x 60 x 3.703 x 10-4
= 1.99962g.
=2.0g
17
When a certain a.c supply is connected to a lamp, it lights with the same brightness as it does with a 12 V d.c battery. Then r.m.s value of the a.c supply is?
A
12.0 V
B
3.5 V
C
17.0 V
D
8.5
correct option: a
The r.m.s value of an a.c voltage/current is the value of the d.c. voltage/ current that will dissipate the same amount of energy in a given resistance as the a.c. Thus the r.m.s value of the a.c supply is 12v.
Users' Answers & Comments18
An ammeter of resistance 5Ω has a full-scale deflection when a current of 50 mA flows in it. The value of the resistor required to adapt it to measure a current of 5 A is?
A
0.25Ω
B
5.00Ω
C
19.80Ω
D
0.05Ω
correct option: d
R = (igrg)/I-ig = (50 x 10-3 x 5)/5-(50 x 10-3) = (0.25)/4.95 = 0.0505 = 0.05Ω
Users' Answers & Comments19
The motion of smoke particles from a chimney is typical of?
A
random motion
B
circular motion
C
rotational motion
D
oscillatory motion
correct option: a
Users' Answers & Comments20
In an experiment to determine terminal velocity, as the pressure increases, the viscosity off a liquid
A
increases
B
decreases
C
increases then decreases
D
remains constant
correct option: d
Users' Answers & Comments