Posts Tagged ‘electricity’

Current Electricity : Some important Questions and Answers

Current electricity is one of the interesting as well as scoring chapter for the students of Class XII. Please find below a collection of questions and answers commonly asked in various Board Exams

current electricity

A Question from Current Electricity

Pratham asked:

The resistances of 2 bulbs are in the ratio 1:2.if they are joined in series,find the ratio of the energy consumed by the 2 bulbs?

Answer:

When connected in series, the same current flows through each of the resistors. Therefore, the energy dissipated is directly proportional to their resistances. That is, the ratio of energy dissipated will nbe same as the ratio of resistances. (1:2)

Numerical Problems for Practice – Current electricity

1. At room temperature (27 ^oC) resistance of a heating element is 100 ohm. What is the temperature of the element if the resistance is found to be 117 ohm. Given, temperature coeff. of resistance of the material is 1.70 x 10 ^{-14 o}C^-1
2. The ends of a resistance are connected to 19 cells in series, each of resistance 0.1 ohm. The current is found to be 2A. The number of cells is reduced to 15 and an extra resistance of 9.5 ohm is connected in series to the given resistance. The current becomes half. Find the given resistance and the emf of each cell.

Current electricity – Numerical problems

1. In a potentiometer arrangement a cell of emf 1.25 V gives a balance point at 35 cm length of the wire. If the cell is replaced by another cell, the balance point shifts to 63 cm. What is the emf of the second cell?

E1= 1.25 V

l1 = 35 cm

l2 = 63 cm

E1/E2 = l1/l2

E2 = l2E1/l1

E2 = 63 x 1.25/35

E2 = 2.25 V (Ans)

A Problem for Practice

A storage battery of emf 8 V and internal resistance 0.5 ohm is charged by 120V dc supply using a resistor 15.5 ohm in series. What is the terminal voltage of the battery during charging?

(Try to solve this problem and post your responses as comment to this post)

Hint: During charging; V = E +Ir

Resistance and Resistivity

Simran Asked

“Two wires A and B of equal lengths,different cross-sectional areas and made of same metal a)name the property which is same for both the wires. b)name the property which is different for both the wires”

Answer:

Since both the wires are of same metal, the resistivity will be same for both whereas since the dimensions (Area of cross section here) are different, the resistance will be different

Potential Difference

Pawan Asked

“What is meant by potential difference?”

Answer:

“Potential Difference between two points is the difference in Potential between the two points and is equal to the work done per unit charge ion carrying a positive test charge from one point to another against the electric field and without any acceleration”