To solve the problem of finding the effective e.m.f. and internal resistance of four cells connected in parallel, we need to understand how cells behave when connected in this manner. ### Step 1: Understanding e.m.f. in Parallel When cells are connected in parallel, the effective e.m.f. (electromotive force) of the combination remains the same as the e.m.f. of one individual cell. This is because each cell provides the same voltage, and they all contribute equally to the voltage across the terminals. - **Given:** Each cell has an e.m.f. of 1.5V. - **Effective e.m.f. (E)** = 1.5V (since all cells are identical). ### Step 2: Understanding Internal Resistance in Parallel The internal resistance of cells connected in parallel behaves differently than their e.m.f. The total internal resistance (R) of the combination can be calculated using the formula for resistors in parallel: \[ \frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \frac{1}{R_4} \] Where \( R_1, R_2, R_3, R_4 \) are the internal resistances of the individual cells. Since all four cells have the same internal resistance of 4Ω, we can simplify this to: \[ \frac{1}{R_{\text{total}}} = \frac{1}{4} + \frac{1}{4} + \frac{1}{4} + \frac{1}{4} = \frac{4}{4} = 1 \] Thus, the total internal resistance \( R_{\text{total}} \) is: \[ R_{\text{total}} = 1Ω \] ### Step 3: Summary of Results - **Effective e.m.f. (E)** = 1.5V - **Total internal resistance (R)** = 1Ω ### Conclusion The correct option is **D. 1.5V, 1Ω**. ### Explanation of Other Options - **Option A: 6.0V, 16Ω** - Incorrect because the e.m.f. does not add up in parallel; it remains at 1.5V. The internal resistance calculation is also incorrect. - **Option B: 6.0V, 1Ω** - Incorrect for the same reason as Option A regarding e.m.f. The internal resistance is correctly calculated as 1Ω, but the e.m.f. is wrong. - **Option C: 1.5V, 4Ω** - Incorrect because while the e.m.f. is correct, the internal resistance is not. The internal resistance of the combination is 1Ω, not 4Ω. ### Revision Summary - In parallel connections, the effective e.m.f. remains the same as that of one cell. - The total internal resistance of cells in parallel is calculated using the formula for resistors in parallel. - For four identical cells with e.m.f. 1.5V and internal resistance 4Ω, the effective e.m.f. is 1.5V and the total internal resistance is 1Ω. - Always remember to check the configuration (series vs. parallel) when calculating e.m.f. and resistance.