Question

Assertion :The current flowing through each resistor is same when connected in series. Reason: The voltage drop across each resistor remains the same when connected in parallel.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

Assertion) Current flows in a circuit. In other words, it's the rate of flow of electric charges. Other than $i=\frac{dq}{dt}$, Current is also given by $I=nAE{v}_d$ which says something that it depends upon the drift velocity of electrons. The drift velocity is the average velocity between two successive collisions. This velocity prevents the electrons from accelerating continuously. Ok. Let's consider a circuit with three resistors with resistances in an increasing order $R_1;R_2;R_3$.

First, current enters $R_1$. After some collisions (causes heat generation), it exits the resistor. Now, the same current enters and exits $R_2$ and $R_3$ in the same manner. The rate of flow of charges is always the same (the current entered and exited the resistors with same magnitude). Only the drift velocities vary in different resistors.

If the same are connected in parallel (Now, we look into the resistors), current flows through $R_3$ easily. Because, $R_3$ requires a lesser $v_d$ (i.e) Electrons entering $R_3$ would exit within a small period of time relative to the other two (thereby increasing the rate). As a result, larger current would be observed.

Reason) Voltage is simply the energy per unit charge in both electrostatics and current electricity. Let's assume that the electrons have some energy and they pass through the series of resistors.

When the electrons encounter collisions within the resistor $R_1$, they lose their potential (which is referred to as "voltage drop") accordingly with their drift velocity (i.e) number of collisions which evolves as heat (depends upon the resistance of each). The remaining potential is still present in those electrons which drops across other resistors. Thus, the sum of each potential drop gives the total potential in that circuit.

As in case of parallel circuit, current has divided. Now, though the charges are taking different paths, they have the same potential (energy). Hence, the potential drop across each resistor would be the same.

So, Assertion and Reason both are coorect but Reason is not the correct explanation for Assertion.