The correct option is
A is true but R is false
Explanation
An ammeter is an instrument used to measure the magnitude of electric current flowing through a circuit. The manner in which it is connected and its internal resistance are critical design features that ensure accurate measurement without disrupting the circuit's operation.
Statement-wise Analysis:
- Assertion (A): Correct
Current is the flow of charge per unit time. In a series combination, the electric current remains the same through all components. To measure the current flowing through a specific branch or component, the ammeter must be connected in series with that component so that the entire current passes through the instrument. - Reason (R): Incorrect
When an ammeter is connected in series, its resistance adds to the total resistance of the circuit. According to Ohm’s Law ($I = V/R$), if the total resistance increases significantly, the current flowing in the circuit will decrease. To measure the current accurately without altering its value, an ammeter must have very low resistance (ideally zero). A high resistance would cause a significant voltage drop across the ammeter and reduce the current it is trying to measure.
Key Takeaway:
An ammeter is always connected in series and must have low resistance. Conversely, a voltmeter is connected in parallel and must have high resistance.