# Physics BSc. (TU Four Years) Question Paper 2065 | First Year

## Subject : Physics I

*“Candidates are required to give their answers in their own words as for s practicable.*

“The figures in the margin indicate full marks.”

Year: 2065

Section A

**Long answer question**

1.What is meant by Galilean invariance? Show that distance and acceleration are

invariant to Galilean transformation, velocity is not invariant.

(2+1.5+1.5+2)

2.It is given that the potential energy of a system is rotationally invariant. What do

you mean by rotational invariance? Show that angular momentum is conserved for

such a system. (3.5+3)

3.(a)Discuss the analogy between liquid flow and current-flow and hence, derive an expression for liquid- flow through capillaries in series. (4)

(b) State Gauss’s law and use it to show that excess charge of a charged conductor resides on its outer surface. (3)

4.(a)Discuss the analogy between liquid- flow and current -flow and hence, derive an expression for liquid flow through capillaries in series.

(4) State Gauss’s law and use it to show that excess charge of a charged conductor resides on its outer surface. (3)

(5). Derive the expression for energy density in the magnetic field.

6. Explain the empirical basis for writing the Maxwell’s equations and write them.

**Section “B”**

**Short answer Questions:**

**Answer any eight:**

a. A proton is accelerated through a potential difference 50V and the n it is allowed cross a field free region 7.5m long. Find the time required to cross this distance.

8.Find the height of geostationary satellite (as viewed by an observer on the earth’s

surface); given g=9.8 ms on the earth’s surface, R= 6.38 x 105m.

9. The potential energy for the Vander Waals force between two atoms is given by

U(X) = , where x is the distance between the atoms and a and b are positive constants. Calculate the force between the two atoms and plot it against x.

10. A parallel LCR circuit has L= 8mH, C= 10 μF and R= 0,5Ω. Calculate the natural

frequency and quality factor.

11. A water drop of radius 0.01 mm is falling through air neglecting the density of air as

compared to the water, calculate the terminal velocity of the drop (ɳ for air = 1.8 x

12. Two point charges of and are located at the origin and at (a, 0, 0) respectively Find the point where electric field vanishes.

13.Two parallel conducting platees are separated by the distance d and potential

differenceᐃ ψ. A dielectric slab of dielectric constant k is and of uniform thickness

is tightly fitted between the plates. Find the electric field in the dielectric.

14.What is the capacitance of a capacitor that can store 800 J at 800 V? Suppose the capacitor has parallel plates separated by