These are instruments which are used in physics for various circuit construction and experimental purpose. We cannot make circuits without these apparatus and instruments. Learners must understand these apparatus structure and construction.

Moving coil galvanometer

The moving coil galvanometer consists of a fine coil of wire pivoted on jeweled points between the pole pieces of a powerful permanent magnet. The movement of the coil is controlled by a fine spring.

A long light pointer is attached to the coil. The pointer moves over a circular scale with a zero at the centers.

When a current is sent through the coil, it is deflected and the pointer moves over the scale. The direction of motion of the pointer depends on the direction of the current.

The extent of the movement is directly proportion to the current. This galvanometer can measure very small currents of the order of micro amperes. This can be modified into an ammeter to measure currents in amperes or into a voltmeter to measure potential differences in volts.

Ammeter

The ammeter is a modified form of moving coil galvanometer designed to read current directly in amperes. The scale is graduated in amperes. A moving coil galvanometer can be converted into an ammeter by connecting a suitable low resistance across the terminals.

The two resistances connected in parallel across the coil of the galvanometer are called the ‘shunt’. The ammeter is a low resistance instrument. It is always connected in series with the circuit, the current in which is to be measured.

Voltmeter

The voltmeter is used to measure the potential difference between two points in an electrical circuit. In construction, it is similar to an ammeter, but it has a high resistance connected in series with the coil.

The voltmeter is graduated to read the Potential Difference in volts. It should always be connected in parallel with the two points across which the Potential Difference is required.

A moving coil galvanometer can be converted into a voltmeter by connected a high resistance in series with it.

Rheostat

The rheostat is an adjustable resistance used in electrical circuits. It is used to adjust the current in the circuit by varying the resistance. It consists of porcelain tube over which is wound tightly a uniform resistance wire.

The current enters it at one end of the coil and leaves through a sliding contact another top end to which the other terminal is attached. The resistance between the slider and the end where the current enters is included in the circuit.

Resistance box

A resistance box enables a known resistance to be included in a circuit. There are two types of boxes, plug type and the dial type. By removing a plug or turning the dial, the required resistance can be introduced in the circuit in which the box is connected.

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Some basic physics instruments - school and college students must understand - Old to New Reviewed by knowledge people creators on January 01, 2020 Rating: 5