PHYSICS LAB ACTIVITY BOOK
(with Free Practical Based MCQ Booklet)
1. RHEOSTAT & RESISTANCE COIL :
It consists of a non-conducting tube on which insulated wire made of constantan, eureka or manganin is wound. The ends of A and B of the wire provides two terminals. There is a metal rod(R) with a pressing knob touching the wire AB provides the third terminal S to use it as variable resistance between A and the movable point S or between B and movable point S. It can also be used as a potential divider arrangement by connecting a battery of voltage V between A and B , The desired voltage can be obtained between a fixed end point A and the moving point S by changing the length of wire AS.
2. RESISTANCE COIL :
It is a double folded wire made of constantan or manganin and is of calculated length, wound on a plastic or wooden reel which is enclosed in an ebonite box. The free ends of the wire are connected to two metallic terminals provided at the top of the ebonite box. It is free from self-induction effects. It has very small temperature coefficient of resistance. It is made up of an alloy with Cu 60% + Ni 40%,/OR Cu 83% + Mn 13% + Ni 4%.AIM —To determine resistance per cm of a given wire by plotting a graph of potential difference versus current.
A voltmeter, an ammeter, unknown resistance wire, rheostat, plug key, a dry cell or a battery and connecting wires.
Ohm’s law states that the physical conditions like temperature, stress, strain etc., remaining unchanged, the current flowing through a conductor is always directly proportional to the potential difference across its two ends or the ratio of potential difference between the ends of the conductor to the current flowing through it is constant.