Current Electricity - Multiple Choice Questions

Q1. When Wheatstone bridge is in balance condition, the current through galvanometer will be

• Maximum
• Minimum
• Zero
• Depends upon the type of galvanometer.

Solution

When the bridge is in balance condition, no current will flow through the galvanometer because potential difference between the two ends of galvanometer becomes same.

Q2.

Three resistors of 4 Ω, 12 Ω, and 6 Ω are connected in parallel. No. of 12 Ω resistors required to be connected in parallel to reduce the total resistance to half of its original is

• 2
• 3
• 6
• 12

Solution

The total resistance of 4 Ω, 12 Ω, and 6 Ω in parallel is 2 Ω. Suppose n is the number of 12-ohms resistor required to be connected to reduce the total resistance to half the original value, i.e. R’=2/2 = 1 Ω. The total resistance of n 12- ohms resistors in parallel is 12/n.

   

Q3.

There are n cells in a circuit. Each cell is of emf 1.5 V and has internal resistance of 0.5 Ω. When they are connected in series with a resistance of 20 Ω, they send a current of 0.6 A through the circuit. What is the value of n?

• 5
• 10
• 15
• 20

Solution

Q4.

A circuit has 5 A current flowing through it. When an additional resistance of 2 Ω is inserted in the circuit, the current through it drops to 4 Ω. What is the initial resistance of the circuit?

• 4 Ω
• 2 Ω
• 8 Ω
• 16 Ω

Solution

Q5. Ohm's law states that

• V = I/R
• V = R/I
• V = IR
• V = I²R

Solution

V = IR

Q6. The type of materials whose resistivity is affected on adding the impurity is known as

• Conductor
• Insulator
• Semiconductor
• Iron alloys

Solution

The resistivity of semiconductors decreases on adding the impurity.

Q7.

The current in a coil of resistance 90 ohms is to be reduced by 90 percent. What value of resistance should be connected in parallel with it?

• 9 Ω
• 100 Ω
• 90 Ω
• 10 Ω

Solution

The resistance is connected in parallel. Hence, voltage across the required resistance S and 90 Ω is the same, i.e.

0.9 I × S = 0.1 I × 90

S = 90/9= 10 Ω

Q8. Copper is not used as potentiometer wire because

• Copper is soft and flexible
• Copper has high temperature coefficient of resistance and small resistivity
• Copper has high resistivity
• Copper has low temperature coefficient of resistance

Solution

Copper has low resistivity and a high temperature coefficient of resistance and hence we do not use it in potentiometer.

Q9.

Which of the following is an ohmic conductor?

• diode
• LED
• Thyristor
• Metal conductor

Solution

Only the metal conductors obey Ohm's law.

Q10.

Three equal resistors each of resistance r are connected to form a triangle. The equivalent resistance across any two corners of the triangle is

• 2r
• r/3
• 2r/3
• 3r

Solution

In triangle circuit two sides are in series and are parallel to third side. Hence, its equivalent resistance will be:

Q11.

Wheatstone bridge is used to measure

• emf
• potential
• resistance
• current

Solution

Wheatstone bridge is used to measure an unknown resistance.

Q12.

Two cells of 1.25 V and 0.75 V are connected in parallel. The effective voltage will be

• 0.75 V
• 1.25 V
• 2.00 V
• 0.5 V

Solution

Using Kirchoff's rules we can see that the voltage available = V₁ - V₂ = 0.5 V

Q13.

A resistance of 2 Ω is connected a across the gap of a metre-bridge (the length of the wire is 100 cm) and an unknown resistance,

x > 2 Ω, is connected across the other gap. The balance point is noticed at l cm from the positive end of the battery.  When these resistances are interchanged, the balance point shifts by 20 cm. Neglecting any correction, the unknown resistance is:

• 3 Ω
• 4 Ω
• 5 Ω
• 6 Ω

Solution

Q14.

What is the maximum current that can be drawn from a cell of emf E and internal resistance r connected to an external resistance R?

• I = E/r
• I = E/R
• I = E/(R+r)
• infinite

Solution

As the maximum current that can be drawn from a cell is for R =0 and it is I = E/r.

Q15.

Two identical cells are connected in series and then in parallel. When connected it series they send a current of 10 A through a 5 Ω resistor and when connected in parallel they send a current of 8 A. What is the internal resistance of each cell?

• 2.5 Ω
• 5 Ω
• 7.5 Ω
• 10 Ω

Solution

Q16.

1 ohm is equal to

• 1 ampere per volt
• 1 volt per ampere
• 1 milliampere per volt
• 1 ampere per millivolt

Solution

R = V/I 

So, one ohm will be one volt per ampere

Q17. Three identical cells, each of 2V and internal resistance of 0.2 ohm are connected in series to an external resistance of 7.4 ohm. The current in the circuit will be

• 0.75 A
• 1.05 A
• 2 A
• 3 A

Solution

Q18.

When the position of cell and galvanometer in a Wheatstone bridge is inter-changed, its balanced condition

• Changes
• Remains unchanged
• Changes and it depends on cell position only
• Changes and depends on galvanometer position only

Solution

When the position of cell and galvanometer in a Wheatstone bridge is interchanged, the balanced condition remains unchanged.

Q19. The total resistance of three parallel resistors is

• R_T = 1/R₁ + 1/R₂ + 1/R₃
• R_T = R₁ + R₂ + R₃
• 1/R_T = 1/R₁ + 1/R₂ + 1/R₃
• 1/R_T = R₁ + R₂ + R₃

Solution

The formula of parallel circuit is 1/R_T = 1/R₁ + 1/R₂ + 1/R₃

Q20.

While traversing a loop we must consider

• resistors and sources of emf
• only resistors
• only sources of emf
• none of the above

Solution

While traversing a loop we must consider resistors and sources of emf.

Q21.

If a wire of resistivity ρ is stretched to double its length. Then its new resistivity will be

• half of the original resistivity
• Four times the original resistivity
• Double the original resistivity
• Remains same

Solution

Resistivity of the material wire depends upon the nature of material and is independent of the dimensions of a wire.

Q22.

Three identical cells, each of 4 V and internal resistance r, are connected in series to a 6 ohm resistor. If the current flowing in the circuit is 2 A. The internal resistance of each cell is

• 0.11 ohm
• 0 ohm
• 0. 12 ohm
• 1.1 ohm

Solution

Total emf = 3 x 4 = 12 V

Total resistance = 6 + 3r

Current in the circuit = 2 A

Using ohms law

2 = 12/ (6 + 3r)

2(6 + 3r) = 12
12 + 6r=12
6r = 12 - 12 = 0
r = 0/6 = 0

Q23.

If a wire of resistivity ρ is stretched to double its length. Then its new resistivity will be

• half of the original resistivity
• Four times the original resistivity
• Double the original resistivity
• Remains same

Solution

Resistivity of the material wire depends upon the nature of material and is independent of the dimensions of a wire.

Q24. The resistance of a wire is r ohms. It is stretched to double its length. The new resistance of the wire in ohms is

• r/2
• 2r
• r/4
• 4r

Solution

Resistance =

Now since the wire is stretched to double its length, the volume of the wire remains same

Q25.

Mobility of charge carriers in a conductor is given by

• drift velocity/ electric field
• (drift velocity)(electric field)
• ( charge of an electron).drift velocity/ electric field
• mass of an electron.(drift velocity/ electric field)

Solution

Mobility of charge carriers in a conductor is given by drift velocity/ electric field

Q26. An electric bulb is rated 220 V and 100 W. Power consumed by it operated on 110 V is

• 25 W
• 50 W
• 75 W
• 90 W

Solution

Resistance of the bulb R = V² / P

And Power consumed at 110 V is = V’² / R

Q27. In a potentiometer a cell of e.m.f 2V gives a balance point at 30cm. If the cell is replaced by another cell and the balance point shifts to 60cm.What is the e.m.f of the other cell?

• 0.4 V
• 4.0 V
• 40.0 V
• 0.04 V

Solution

Q28. The negative sign in calculations involving circuit problem signifies

• Wrong result
• Nothing
• Current is in a direction opposite to the assumed direction
• Use of wrong factor

Solution

Negative sign in answer does not mean a wrong answer. It indicates that current are in opposite direction to assumed direction.

Q29. Under what condition, the current drawn from the cell is maximum?

• R = 0
• R = r
• R > r
• R < r

Solution

The maximum current can be drawn from a cell if the external resistance R = 0.

Q30.

The resistance of hot tungsten filament is about 10 times to that of cold tungsten filament. What will be the resistance of 100 W and 220 V lamp when not in use?

• 484 ohm
• 4.84 ohm
• 4840 ohm
• 48.4 ohm

Solution

R = V² / P , cold resistance = R / 10

Ω

Thus, when the lamp is not in use, the resistance will be

Ω

Q31.

Sensitivity of potentiometer can be increased by

• Increasing the length of potentiometer wire and reducing current.
• Increasing voltage
• Decreasing length of potentiometer wire
• Increasing current in circuit

Solution

Sensitivity of potentiometer can be increased by increasing the length of the potentiometer wire and by reducing the current in the circuit by using a rheostat. Both the methods help in decreasing the potential gradient, and thereby increasing the resistivity.

Q32. When numbers of cells in series combination are increased, the current of the circuit will

• Decrease
• Increase
• Remain same
• Depends on the resistance of the circuit

Solution

The current of the circuit will increase when numbers of cells in series are increased.

Q33.

The internal resistance of dry cells is ________than the common electrolytic cells.

• lower
• higher
• equal to
• lower or equal

Solution

It is much higher than the internal resistance of common electrolytic cells.

Q34.

Which statement is true about the conventional flow of current?

• It flows from positive to negative because protons move inside the battery from positive to the negative terminal.
• It flows from positive to negative terminal, because electrons move from negative to positive terminal inside a battery.
• It flows from negative to positive because protons move from negative to positive terminal inside the battery.
• It flows from negative to positive because the electrons move from negative to positive terminal inside the battery.

Solution

It is by convention that the current flows from positive to negative, whereas in reality electrons flow from negative terminal of battery to the positive terminal of battery.

Q35.

Meter Bridge or Slide Wire Bridge is a practical form of

• Potentiometer
• Voltmeter
• Ammeter
• Wheatstone bridge

Solution

Meter Bridge or Slide Wire Bridge is a practical form of Wheatstone bridge.

Q36.

Kirchhoff's second law is applicable only to

• Open loops
• Closed and open loops
• Closed loops
• Mechanical systems

Solution

Kirchhoff's second law is applicable to closed circuits only as we form the equations using the loop and sign convention.

Q37. When number of cells in series combination is increased, the voltage of the circuit will

• Decrease
• Increase
• Remain same
• Depends on the internal resistance of the battery

Solution

The voltage of the circuit will increase, when more cells are connected in series.

Q38. In a metre bridge experiment null point is obtained at 20 cm from one end of the wire when resistance X is balanced against abother resistance Y. If X < Y, then where will be new position of the null point from the same end, if one decides to balance a resistance of 4X against Y

• 50 cm
• 80 cm
• 40 cm
• 70 cm

Solution

Q39.

If the internal resistance of a cell is 20 ohm and resistance of the circuit is also 20 ohm. Will the current remain same whether the given n identical cells are in series or in parallel?

• Can't predict
• None of the above
• yes
• No

Solution

Since for same current R = r.

Q40. Current provided by a battery is maximum when

• internal resistance is equal to external resistance
• internal resistance is greater then external resistance
• internal resistance is less than external resistance
• none of these

Solution

Current provided by a battery is maximum when internal resistance is equal to external resistance.