31.

A working transistor with its three legs marked P, Q and R are tested using a multimeter. No conduction is found between P and Q. By connecting the common (negative) terminal of the multimeter to R and the other (positive) terminal of P or Q, some resistance is seen on the multimeter. Which of the following is true for the transistor?

• It is an n-p-n transistor with R as base

• It is a p-n-p transistor with R as collector

• It is a p-n-p transistor with R as emitter 

• It is a p-n-p transistor with R as emitter 

A student measures the focal length of the convex lens by putting an object pin at a distance ‘u’ from the lens and measuring the distance ‘v’ of the image pin. The graph between ‘u’ and ‘v’ plotted by the student should look like

Suppose an electron is attracted towards the origin by a force k/r where ‘k’ is a constant and ‘r’ is the distance of the electron from the origin. By applying Bohr model to this system, the radius of the nth orbital of the electron is found to be ‘rn’ and the kinetic energy of the electron to be Tn. Then which of the following is true?

• T_n ∝ 1/n², r_n ∝ n² 

• T_n independent of n, r_n ∝ n

• T_n ∝ 1/n, r_n ∝ n 

• T_n ∝ 1/n, r_n ∝ n 

In the circuit below, A and B represent two inputs and C represents the output. The circuit represents

• NOR gate

• AND gate

• NAND gate

• NAND gate

An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distance are measured by 

• a vernier scale provided on the microscope

• a standard laboratory scale 

• a meter scale provided on the microscope 

• a meter scale provided on the microscope