Test: Current Electricity (15 Nov) - JEE MCQ

Kirchhoff’s loop rule is based on the principle of conservation of energy. The work done in transporting a charge in a closed loop is zero. The algebraic sum ( since potential differences can be both positive and negative) of potential differences around any closed loop is always zero.

The balance point of the Wheatstone’s bridge is determined by the ratio of the resistances. The change in the emf of the external battery will have no effect on the balance point.
 

Explanation:

• Initial Balanced Wheatstone Bridge: In the initial balanced Wheatstone bridge configuration, the emf of the cell is 1.46 V and all four resistors R1, R2, R3, and R4 are set to specific values to achieve balance.


• Replacement of Cell: When the cell is replaced by another cell with an emf of 1.08 V, the balance of the Wheatstone bridge is disrupted.


• Requirement for Rebalancing: In order to rebalance the Wheatstone bridge with the new cell of emf 1.08 V, no resistance needs to be changed.


• Reasoning: The balance of the Wheatstone bridge is determined by the ratio of the resistances in the bridge arms and not by the absolute values of the resistances. As long as the ratio of the resistances remains the same, the balance will be maintained regardless of the emf of the cell.


• Conclusion: Therefore, in this scenario, no resistance needs to be changed to obtain the balance again with the new cell of emf 1.08 V.


 

According to Ohm’s law, V = IR. Therefore R= V/I

We want the Voltage difference V_AB.
let A and B be open and not connected to any thing.
There is a current that flows from cell of larger emf to the cell of small emf.
Call that current as  I Amperes.

1.25 V - 0.75 V - I * R2 - I * R1 = 0

I = 0.5 / (R1+R2)
V_AB =  -0.75 - I * R2 =  - 0.75 - 0.5 * R2 / (R1+R2)

= - (0.75 R1 + 1.25 R2) / (R1+R2)

= - ().75 * 1 + 1.25 * 1) / (1 + 1)  volts

=  - 1 volts

1. Current: This is a general term for the flow of electric charge. It can refer to any type of charge flow, not specifically electrons.

2. Electronic current: This specifically refers to the flow of electrons through a conductor.

3. Conventional current: This is the flow of positive charge and is considered to flow from the positive side to the negative side of a power source. Historically, this was defined before the discovery of electrons, so it is opposite to the direction of electron flow.

4. Photonic current: This is not a standard term in electrical engineering or physics. It might refer to currents related to photons in some contexts, but it is not related to the flow of electrons.

So, if you are referring to the flow of electrons specifically, electronic current is the accurate term.

The connecting metal strips include a small resistance in the circuit called the end resistance.On reversing the current, the end resistance tends to get cancelled out.

Power P= V²/R​
If length reduced 10% then new resistance of filament will be R′.
R′=R−10% of R
R′=0.9R
Now new power of heater is P2​
P_2​= V²​​/R′ = V²/0.9R​​=1.1P
% increase power=11%

According to Ohm’s law, V=I R. Therefore R=V/I

Ohm’s law states I is proportional to V.This holds good at steady temperatures and for the flow of constant current.

Potentiometer is a long wire of uniform cross section made of manganin.

1. Newton is SI Unit of Force
2. Joule is SI Unit of Work Done
3. Coulomb is SI Unit of Charge
Hence, the unit of current is Ampere.

No current passes through the Galvanometer in the bridge balance condition.Therefore, the resistance between B and D is infinite.

• Both potentiometer and voltmeter are devices to measure potential difference.
• EMF is the terminal p.d between the electrodes of a cell in open circuit, i.e., when no current is drawn from it.
• Potentiometer measures the potential difference using null deflection method, where no current is drawn from the cell; whereas voltmeter needs a small current to show deflection.
• So, accurate measurement of p.d is done using a potentiometer.

• An electric field exists in the electrolyte between the positive and negative terminals of the battery.
• In the external circuit, the current flows from the positive electrode to the negative electrode.
• To maintain continuity, in the electrolyte, the current (positive charges) flow from the negative electrode (lower potential) to the positive electrode (higher potential).
• Work done by the source in taking unit positive charge from lower to higher potential is called electromotive force.

The electrons in a conductor have random velocities and when an electric field is applied, they suffer repeated collisions and in the process move with a small average velocity, opposite to the direction of the field. This is equivalent to positive charge flowing in the direction of the field.