Electricity Test

Result

Electricity Test - 8

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Weekly Quiz Competition

Question 1
1 / -0

If the resistance of a conductor in a given circuit is increased, then the current will

A
increase

B
decrease

C
remain the same

D
first increase and then decrease

Solution

We know V = IR, where V is the voltage, I is the current and R is the resistance.
I is inversely proportional to R, as electric potential is constant. So, if the resistance of a conductor is increased, the current will decrease.
Question 2
1 / -0

A wire has a resistance of 1 Ω. It is stretched to double its length. The resistance of the wire will be

A
1 Ω

B
2 Ω

C
4 Ω

D
16 Ω

Solution

Here the length of the wire is doubled but the volume of the wire remains same
Volume =
L' = 2L
Resistance of the wire is given by

R' = 4 × 1 = 4 Ω
Question 3
1 / -0

When an electric heater is switched on, the current (i) flowing through it is plotted against time (t). Taking into account the variation of resistance with temperature, which of the following best represents the resulting curve?

A

B

C

D

Solution

The filament of the heater reaches its steady resistance when the heater reaches its steady temperature, which is much higher than the room temperature The resistance at room temperature is than much lower than the resistance at its steady state When the heater is switched on it draws a larger current than its steady state current As the filament heats up, its resistance increases and current falls to steady state value.
Question 4
1 / -0

What value must the resistor R₁ have in order that the resistance between the terminals A and B is R?

A

B

C

D

Solution

Resultant of R and R₁ is in parallel with other resistor R.
Resultant of R and R₁= R + R₁
This is in parallel with R.
Hence, equivalent resistance = =
And this equivalent resistance is in series with R₁.

Hence, net resistance =
And this must be R.

So,
(R₁ + R)R + R₁² + 2RR₁ = RR₁ + 2R²
2R₁R + R₁² = R²
R₁² + 2R₁R - R²Solving for R₁, we get
R₁ = ( - 1)R
Question 5
1 / -0

When a body is negatively charged by friction, it means the body has

A
lost some electrons

B
lost some protons

C
acquired excess of electrons

D
acquired excess of protons

Solution

Whenever two different materials rub against each other, it is likely that one will leave with more electrons than it started with. Electrons are negatively charged; so when a body is negatively charged by friction, it means the body has acquired excess of electrons.
Question 6
1 / -0

A current of 5 amperes is flowing through a resistance. Charge appearing through the resistance per second is

A
50 coulombs

B
5 coulombs

C
10 coulombs

D
4.2 coulombs

Solution

Since, I =
I = 5 amperes (where I is the current flowing through the resistance, t is the time and is t = 1 s amount of charge passing)

= 5 coulombs
Question 7
1 / -0

The effective resistance between A and B is

A
9

B
1

C
6

D
3

Solution

Let R₁ = 2.5 + 0.5

R₁ = 3 (Because 2.5 and 0.5 are in series)
Let R₂ = (1.5 + 1.5) (Because they are in series)
= 3
(Because they are all in parallel)
After putting the values of R₁ and R₂, we get
R₃ = 1
Question 8
1 / -0

In the circuit shown below, some potential difference is applied between A and B. If the equivalent resistance between A and B is R, then which of the following is correct?

A
^{_{No current flows through the 5}_resistor}

B
^{_{R = 15}}

C
^{_{R = 12.5}}

D
^{_{R =}}

Solution

No current flows through the resistor.
The given circuit is a Wheatstone bridge circuit.
It can be transformed as shown in the given figure.
Since the ratio of the resistances is equal, i.e. ,
So, the voltage between the two midpoints (A and B) will be zero and no current will flow through .
Question 9
1 / -0

An electric current from a battery of 6 V passes through a circuit having three lamps of resistances 2 , 3 and 4 joined in parallel. The current passing in the 4 lamp is

A
2.5 A

B
4.5 A

C
6.5 A

D
1.5 A

Solution

Consider the following figure:

We know, V = IR
Voltage = 6 V, R = 4
V = I₃ R
6 = I₃4
I₃ = A
I₃ = 1.5 A
Question 10
1 / -0

If a 60 W bulb is lit everyday for 5 hours, the consumption of energy in a month of 30 days will be

A
9 kWhr

B
90 kWhr

C
9 Jhr

D
90 Whr

Solution

We know, Power =
P = 60 W
T = 5 hours for 30 days
= 5 ×30
= 150 hours
Work = P × T
= 60 × 150
= 9000
= 9 kWhr
Question 11
1 / -0

Two very long parallel wires carry equal currents in the same direction. They are found to attract each other with a force F. If the current in each wire is halved, the force of attraction will be

A
F

B
2 F

C
F

D
F

Solution

Let the previous force F₁ =
When we will half the current in each wire, the new force F₂ will be =
Question 12
1 / -0

The induced emf produced when a magnet is inserted into a coil does not depend upon

A
number of turns in the coil

B
resistance of the coil

C
magnetic moment of the magnet

D
speed of approach of the magnet

Solution

The induced emf produced when a magnet is inserted into a coil does not depend upon resistance of the coil.
Question 13
1 / -0

The number of turns in the primary and the secondary coils of a transformer are 1000 and 3000, respectively. If the primary coil is connected to 80 volt ac, then potential difference per turn of the secondary coil is

A
240 V

B
24 V

C
0.24 V

D
0.08 V

Solution
Question 14
1 / -0

R_S is the shunt resistance, ig is the maximum permissible current through galvanometer, Rg is resistance of galvanometer, and I is the current to be measured by the ammeter. R_s is given by

A
R_S =

B
R_S =

C
R_S =

D
R_S =

Solution

R_Sis the shunt resistance, ig is the maximum permissible current through galvanometer, Rg is resistance of galvanometer, and I is the current to be measured by the ammeter. R_s is given by
Question 15
1 / -0

ABCD is a square loop made of a uniform conducting wire. A current enters the loop at A and leaves at D. The magnetic field is

A
zero only at the centre of the loop

B
maximum at the centre of the loop

C
zero at all points outside the loop

D
zero at all points inside the loop

Solution

ABCD is a square loop made of a uniform conducting wire. A current enters the loop at A and leaves at D. The magnetic field is zero only at the centre of the loop
Question 16
1 / -0

A charge q is placed at the centre of the line joining two equal charges Q each. The system of the three charges will be in equilibrium, if q is equal to

A
–Q/2

B
–Q/4

C
+Q/4

D
+Q/2

Solution

A charge q is placed beween two charges QThe three charges will be in equilibrium if no force is acting on each charge.The charge q is in equilibrium if the force acting on it by charge Q on one side is equal and opposite to the force acting on the charge q by the charge Q placed on the other side of charge q. i.e

q = -Q/4
Question 17
1 / -0

The utility of a safety fuse in an electric circuit depends on its low

A
melting point

B
strength

C
resistivity

D
conductivity

Solution

The utility of a safety fuse in an electric circuit depends on its low melting point.
Question 18
1 / -0

The peak voltage of the AC supplied in India is

A
220 /V

B
/ 220 V

C
×220 V

D
None of these

Solution

The peak voltage of the AC supplied in India is× 220 V.
Question 19
1 / -0

Three cells of EMF 1.5 volts each and internal resistance of 1 ohm are connected in parallel. This combination is used to send current through an external resistance of 0.001 ohm. What is the value of the current?

A
1.5 A

B
0.5 A

C
4.5 A

D
3.0 A

Solution

The three cells are connected in parallel. Voltage remains the same in a parallel combination. Hence, voltage will be the same across all the cells and the external resistance. Current passing through the external resistance, i = 1.5/1.001 = 1.499 A ≈ 1.5 A
Question 20
1 / -0

If a piece of metal was thought to be a magnet, which one of the following observations would offer conclusive evidence?

A
It attracts a known magnet

B
It repels a known magnet

C
It attracts a steel screw driver

D
None of the above

Solution

If a piece of metal was thought to be a magnet, observations would offer conclusive evidence if It repels a known magnet as repulsion is the sure test of magnetism.