(a) (i) State the principle on which a potentiometer works. How can a given potentiometer be made more sensitive?
(ii) In the graph shown below for two potentiometers, state with reason which of the two potentiometers, A or B, is more sensitive.
(b) Two metallic wires, and of the same material and same length but different cross - sectional of emf. Find the ratio of the drift velocities of free electrons in the two wires when they are connected (i) in series, and (ii) in parallel. 5 marks
(a) (i) The potential difference across any length of wire is directly proportional to the length provided current and area of cross section are constant i.e., E(l) = where is the potential drop per unit length. 1mark
It can be made more sensitive by decreasing current in the main circuit / decreasing potential gradient / increasing resistance put in series with the potentiometer wire. mark
(ii) Potentiometer B mark
Has smaller value of (slope / potential gradient). mark
(b) In series, the current remains the same. mark
I =ne mark
In parallel potential difference is same but currents are different.