NCERT Class 10 Science — Chapter 3: Electricity

The correct Answer is

A, B, C and D

Explanation

The question pertains to the fundamental principles of electrical circuits, specifically the correct placement of common electrical devices (ammeter, voltmeter, fuse, rheostat) within a circuit to ensure their proper function. The placement depends on the device's purpose and its internal resistance characteristics.

Statement-wise Analysis

1. A. Ammeter - series: Correct
   An ammeter is used to measure electric current flowing through a circuit or a component. It has very low internal resistance. To measure the current accurately without significantly altering the circuit's total resistance, an ammeter must be connected in series with the component or circuit branch through which the current is to be measured. This ensures that the entire current passes through the ammeter.
2. B. Voltmeter - parallel: Correct
   A voltmeter is used to measure the potential difference (voltage) across two points in a circuit, typically across a component. It has very high internal resistance. To measure the potential difference accurately without drawing significant current from the main circuit, a voltmeter must be connected in parallel across the component whose voltage is to be measured. This ensures that the current flowing through the voltmeter is negligible.
3. C. Fuse - series: Correct
   A fuse is a safety device designed to protect electrical circuits from overcurrent. It contains a wire or filament that melts and breaks the circuit when the current exceeds a safe level. For a fuse to effectively interrupt the current flow and protect the entire circuit, it must be connected in series with the live wire of the circuit. If connected in parallel, it would not break the main circuit path.
4. D. Rheostat (variable resistance) - in series to regulate current: Correct
   A rheostat is a variable resistor used to control the current in a circuit. By changing its resistance, the total resistance of the circuit can be altered, thereby regulating the current (according to Ohm's Law, I = V/R). To regulate the current flowing through a circuit or a specific part of it, the rheostat is typically connected in series. This allows its variable resistance to directly impact the total resistance of the current path.

Key Takeaway

The correct connection of electrical devices (ammeter in series, voltmeter in parallel, fuse in series, rheostat in series for current regulation) is determined by their function and internal resistance characteristics to ensure accurate measurement or effective operation without disrupting the circuit.