DIP202 : APPLIED PHYSICS
UNIT- IV
1. A balloon, initially neutral, is rubbed with fur until it acquires a net charge of - 0.60nC. (a) Assuming that only electrons are transferred, were electrons removed from the balloon or added to it? (b)How many electrons were transferred? [3.7 * 10^9]
Ans: ; positive charge Charge on one electron
(a) As the balloon is positively charged, hence electrons are removed from the balloon
(b)
2. If a charge of 105 C flows in 15 sec, calculate the current.
Ans:
3. Calculate the number of electrons which are required to carry a charge of 105C. Ans:
4. Two charges, 5 C and 15 C are separated by 10 cm. What is the force between them?
Ans: ; ;
5. Find force between a proton and an electron placed at the distance 1 µm.
Ans: The force between two oppositely charged particles is attraction and its value is Charge on electron
Charge on proton Distance
6. If the electrical force of repulsion between two 1-C charges is 10 N, how far apart are they?
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7. Two +1 C charges are separated by 30000 m, what is the magnitude of the force?
Ans:
8. What is the force between two small charged spheres having charges of 2 ×10-7C and 3 × 10–7C placed 30 cm apart in air?
Ans: Charge on the first sphere, q1 = 2 × 10−7 C Charge on the second sphere, q2 = 3 × 10−7 C Distance between the spheres, r = 30 cm = 0.3 m Electrostatic force between the spheres is given by the relation:
Hence, force between the two small charged spheres is 6 × 10−3 N. The charges are of same nature. Hence, force between them will be repulsive.
9. A small charge of 6 mC is found in a uniform electric field of 2.9 N/C. Determine the force on the charge.
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10. Find the electric field acting on a 2 C charge if an electrostatic force of 10500 N acts on the particle.
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11. What is the electric field strength at a distance of 10 cm from a charge of 2 μC?
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12. Two point charges qA = 3 μC and qB = –3 μC are located 20 cm apart in vacuum. What is the electric field at the midpoint O of the line AB joining the two charges?
Ans: Distance between A & B = 20 cm; AO = OB = 10 cm = 0.1 m Electric field at O due to charge
Magnitude of Electric field at O due to charge
Since & are working in the same direction, total electric field at O
13. Consider a uniform electric field . Calculate flux of this field through a square of 10 cm on a side whose plan is perpendicular to this field.
Ans: ;
Area of square As the plan of square is perpendicular to electric field Electric flux though the plane is given by
| || |
14. A point charge of 2.0 μC is at the centre of a cubic Gaussian surface 9.0 cm on edge. What is the net electric flux through the surface?
Ans: q = Net charge contained inside the cube = 2.0 μC = 2 × 10−6 C ε0 = Permittivity of free space = 8.854 × 10−12 N−1C2 m−2 Net electric flux through the cubic surface is given by
15. Three charges +7 C, -8 C, +9 C are placed inside a sphere. Find the magnitude and direction of the flux passing through the sphere.
Ans: q = Net charge contained inside the cube = 7-8+9 = 8 C Net electric flux through the cubic surface is given by
16. Find the value of the potential due to an electric charge of 8 nC at 52 cm from this charge.
Ans:
17. How much work is done in moving a charge of 2 coulombs from a point at 118 volts to a point at 128 volts?
Ans: Potential difference Work done
18. Calculate the electric potential at the surface of the silver nucleus having radius 3.4 × 10-14 m. The atomic no. silver is 47 and charge on the proton = 1.6 × 10-19 C.
Ans: ;
19. A positive charge of 1nC is located at a point. What is the work done if a unit positive charge is carried around this charge along a complete circle of radius 0.1m about this point?
Ans: As all the points around this charge along a circle will be on equipotential surface Hence the work done = Zero (0)
20. If you pass 500 mA of current through a bulb, how many electrons will pass through it in five minutes?
Ans: Current Time
Charge on one electron
Electrons
21. Calculate the current supplied by a cell if the amount of charge passing through the cell in 2 minutes is 240 C?
Ans: ; we know ,
22. What will be the time taken of current drawn of 0.75 microampere by the net value of electric charge as 1 C ?
Ans: Q = 1 C
23. A current of 200 mA flows for 2 minutes. How much charge has passed?
Ans: ;
24. A battery has an emf of 18 volts and supplies a current of 4.5A. What is the resistance of the circuit? How many coulombs leave the battery in 5 minutes?
Ans:
Time
25. Calculate the magnetic flux density at the centre of the solenoid of 1000 turns and 20cm long if a current of 2 A flows in the coil. The diameter of the coil is 4 cm.
Ans: N = 1000; N = 20 cm = 0.2 m; I = 2 A; Magnetic induction due to solenoid
Magnetic flux
26. A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the wire?
Ans: Current in the wire, I = 35 A
Distance of a point from the wire, r = 20 cm = 0.2 m Magnitude of the magnetic field at this point is given as: μ0 = Permeability of free space = 4π × 10–7 T m A–1
Hence, the magnitude of the magnetic field at a point 20 cm from the wire is 3.5 × 10–5 T
27. A long straight wire in the horizontal plane carries a current of 50 A in norths to south direction. Find the magnitude and direction of B at a point 2.5 m east of the wire.
Ans: Current in the wire I =50A
A point is 2.5 m away from the East of the wire.
∴ Magnitude of the distance of the point from the wire, r = 2.5 m. μ0 = Permeability of free space = 4π × 10–7 T m A–1
The direction of the current in the wire is vertically downward.
Therefore by Maxwell’s right hand thumb rule, the direction of the magnetic field at the given point is vertically upward.
28. If the magnetic flux passing through the coil of 100 turns increases 15 weber in 2 seconds then determine the induced emf in the coil.
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29. The magnetic flux through a coil having 100 turns decreases from 5 milli weber to zero in 5 second. Calculate the e.m.f. induced in the coil.
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