The terminals of a battery are joined by a length of resistance wire. Which of the following changes, will decrease the current through the battery?
(i) Connecting an identical wire in series with the first one
(ii) Covering the wire with plastic insulation
(iii) Using a shorter wire of the same material and same thickness
(iv) Using a thinner wire of the same material and same length

Options

A. (i) and (iv)
B. (ii) and (iii)
C. (i) and (iii)
D. (iii) and (iv)

Explanation

To solve the problem, we need to determine which of the given changes will decrease the current flowing through the battery when a resistance wire is connected to it. The current (I) flowing through the circuit can be calculated using Ohm's Law, which states:

\[ I = \frac{V}{R} \]

where:
- \( I \) is the current,
- \( V \) is the voltage of the battery,
- \( R \) is the total resistance in the circuit.

To decrease the current, we need to increase the resistance \( R \). Let's analyze each option:

### Step-by-Step Solution:

1. **Option (i): Connecting an identical wire in series with the first one.**
- When two identical wires are connected in series, the total resistance increases. If the resistance of one wire is \( R \), then the total resistance becomes \( R + R = 2R \).
- Therefore, the current will decrease because the total resistance has increased.
- **Conclusion:** This option will decrease the current.

2. **Option (ii): Covering the wire with plastic insulation.**
- Covering the wire with plastic insulation does not change the resistance of the wire itself. The resistance remains the same, and thus the current will not change.
- **Conclusion:** This option will not decrease the current.

3. **Option (iii): Using a shorter wire of the same material and same thickness.**
- A shorter wire will have a lower resistance compared to a longer wire. Since resistance is directly proportional to length, reducing the length decreases the resistance.
- Therefore, the current will increase.
- **Conclusion:** This option will not decrease the current.

4. **Option (iv): Using a thinner wire of the same material and same length.**
- A thinner wire has a smaller cross-sectional area, which increases the resistance (since resistance is inversely proportional to the area). Thus, if the thickness is reduced while keeping the length the same, the resistance increases.
- Therefore, the current will decrease.
- **Conclusion:** This option will decrease the current.

### Final Answer:
The changes that will decrease the current through the battery are:
- (i) Connecting an identical wire in series with the first one.
- (iv) Using a thinner wire of the same material and same length.