# Magnetic Field and Flux Density

**Topics:**Magnetic field, Electromagnetism, Electric charge

**Pages:**86 (14553 words)

**Published:**July 18, 2013

hi

1. Which of these is not correct as a basic property of electric charges?

(a) Total charges in an insulated system is invariable (b) A charged body is electrically unstable

(c) * A charged body has equal number of positive and negative charges (d) Positively charged body is deficient of electrons

x+q1+q2 = 2 q1

2.Calculate the distance x between charges q1 and q2 shown, given the repulsive force between them as 1.2 x 10-4 N, take the permittivity of vacuum where they were as 8.842x 10 -12 F/M and charge on q1= 1.6x10-19c

(a) * 1.96x10-12M (b) 9.1x104N (c) 16.8x10-4 N. (d) 4.3x108 N

3. Two charges separated by distance x are located in vacuum. One is a quarter in a magnitude of the other. In terms of two charges above Coulomb’s law can correctly represented by:

(a) (b) (c) * (d)

4. Find the ratio (Fe/Fg) of the Coulomb electrical force Fe, to the gravitational force, Fg, between two electrons separated by distance r

(a)*4.2* (b) (c) (d)

5. Two identical balls, carrying equal charge each of mass 0.10g, are suspended freely by two threads of equal length repelled each other so that each thread make angle 300 with vertical line. At equilibrium, calculate the tension in one of the threads.

(Acceleration of gravity pull g = 9.8 m/s2)

(a)* 1.13x10-3 N (b) 6.3x10-6 N (c) 0.41 N (d) 5.1 x10-12 N

6. When two identically charged bodies suspended freely by thread of equal length repel each other all of these forces are acting on one of then except:

(a) Tension (b) Gravitational pull (c)* Coulomb attraction force (d) Repulsive force

D

E

A

C

B

+3mC

-5mC

7. Two charges are separated as shown. Where a third positive charge must be placed if the force it experiences is to be zero?

(a)* At D (b) At C (c) At E (d) At B

8. For series of charges in a closed surface within a vacuum, given that Îo andYe are the electric permitivity and field flux, Gauss’ law can be stated as

(a) (b) (c) (d)

9. One of the following is not a practical use of a capacitor:

(a) To establishment of electric field of a required pattern.

(b) As oscillatory device in circuit.

(c) Used in time-base circuit to initiate an event at a specific time.

(d) To produce and store charges when electric field is lacking.

10. 2mF and 3mF capacitors are both connected in parallel across a 100 V supply line. Calculate the charge on the plates of the capacitors:

(a) 1.5x10-6 C (b) 1.0x10-6 C (c) 5.0x10-4 C (d) 0.7x10-4 C

11. Capacitance of a parallel plate capacitor is in directly proportional to:

(a) The magnitude of the permittivity of the of the dielectric within the plates

(b) The magnitude of the surface area of the plates in the capacitor

(c) Separation of the plates in the capacitor

(d) The magnitude of the voltage applied

12. One plate of a parallel- plate air capacitor has a surface area of 0.2m2 and is separated from the second plate by 0.01m if the electric permittivity of the dielectric used is 8.85x10-12 F/M. Calculate the voltage that will develop 8.85x10-9c charge on its plate.

(a) 7.1x10-2 (b) 50V (c) 4.1V (d) 60.2V

13. A parallel plate air-capacitor has square plate whose area is 0.2m2 and plates separated by 1cm, is connected to 50V battery. Calculate the energy stored in the capacitor if the permittivity of the dielectric used is 8.85x10-12 F/M.

(a) 1.6x10-7 J (b)* 2.21x10-7 J (c) 3.0X10-7J (d) 4.6X10-7J

14. Which of the following is not a characteristic of air-capacitor?

(a) It is stable

(b) * It has high insulation strength

(c) It is simple to make

(d)...

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