Question

1. Two identical charges, each -8.00 x 10-5 C, are separated by a distance of 25.0 cm. Find the electric force between them?

2. What is the electric force exerted on a test charge of 3.86 x 10-5 C if it is placed in an electric field of magnitude 1.75 x 104 N/C?

3. Find the resistance of 134 m of No. 20 copper wire at 20

Answer 1

1) F = kq₁q₂ / r² = 9 * 10⁹ * (8.00 x 10^-5)² / 0.25² = 921.6 N.... Attractive force due to the same nature of charges.

2) F = q * E = 3.86 x 10^-5 * 1.75 x 10⁴ = 0.6755 N ... in the direction of the electric field as the charge is +ve.

3) R = * (l / A) = 1.72 * 10^-6 * (13400 / 2.07 * 10^-2) = 1.1134 ohm

4) energy consumed = Power * time = 100 * 24 * 7 kWh = 16800 kWh

Cost = $ (16800 * 20 / 100) = $ 3360

5) Microwave : Current, i = P/V = 1000 / 120 = 8.33 A ; Resistence, R = V / i = 120 / 8.33 = 14.4 ohm

Florescent Light Bulb : Current, i = P/V = 40 / 120 = 0.33 A ; Resistence, R = V / i = 120 / 0.33 = 360 ohm

Computer : Current, i = P/V = 550 / 120 = 4.583 A ; Resistence, R = V / i = 120 / 4.583 = 26.184 ohm

6) This is because of the fact that the force acting on the beam of electrons due to the magnetic field is perpendicular to the direction of motion. So the work done (as we know is the dot product of the force and the displacement) is 0.

7) B = _oI / 2r = 4 *10^-7 * 7.5 / 2*0.5 = 3 * 10^-6 T

8) BL = _oNI

  ==> I = BL / _oN = 1.5 *10^-3 * 0.15 / 4 * 750 = 2.39 *10^-8 A

9)

An electric generator is a device that converts mechanical energy obtained from an external source into electrical energy as the output.

It is important to understand that a generator does not actually