# Joint Entrance Screening Test (JEST) Past Year Question Papers 2019 Part 3

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## PART- B: 3 Mark-Questions

Q1. A person plans to go from town A to town B by taking either the route with probability or the route with probability (see figure) . Further, there is a probability that R1 is blocked, a probability that R2 is blocked, and a probability that R3 is blocked. What is the probability that he/she would reach town B?

(a)

(b)

(c)

(d)

Q2. What is the change in the kinetic energy of rotation of the earth if its radius shrinks by 1 % ?

Assume that the mass remains the same and the density is uniform.

(a) Increases by 1 %

(b) Increases by 2 %

(c) Decreases by 1 %

(d) Decreases by 2 %

Q3. Analysis the ideal op-amp circuit in the figure. Which one of the following statements is true about the output voltage , when terminal ′ C ′ is connected to point ′ A and then to point ′ B ′ ?

(a) and when ′ C ′ is connected to ′ A and ′ B ′ , respectively

(b) and when ′ C ′ is connected to ′ A ′ and ′ B ′ , respectively

(c) when ′ C ′ is connected to either ′ A or ′ B ′

(d) when ′ C ′ is connected to either ′ A or ′ B

Q4. White light of intensity is incident normally on a filter plate of thickness d. The plate has a wavelength dependent absorption coefficient per unit length. The band pass edge of the filter is defined as the wavelength at which the intensity, after passig through the filter, is and are constants. The reflection coefficient of the plate may be assumed independent of . Which one of the following statements is true about the bandwidth of the filter?

(a) The bandwidth is linear dependent on

(b) The bandwidth is independent of the plate thickness d

(c) The bandwidth is linearly dependent on

(d) The bandwidth is dependent on the ratio

Q5. Consider two concentric spherical metal shells of radii and . The outer shell has a charge q and the inner shell is grounded. What is the charge on the inner shell?

(a)

(b)

(c) 0

(d)

Q6. A wire with uniform line charge density per unit length carries a current I as shown in the figure. Take the permittivity and permeability of the medium to be . A particle of charge q is at a distance r and is travelling along a trajectory parallel to the wire. What is the speed of the charge?

(a)

(b)

(c)

(d)

Q7. Consider a non-relativistic two-dimensional gas of N electrons with the Fermi energy .

What is the average energy per particle at temperature ?

(a)

(b)

(c)

(d)

Q8. The circuit given below is fed by a sinusoidal voltage . Assume that the cut-in voltage of the diode is 0.7 volts and 1 V is a positive dc voltage smaller than 0 V. Which one of the following statements is true about ?