Write down the difference between a semiconductor and a superconductor on the basis of relationship between resistivity and temperature.

Resistivity of a semiconductor increases with the decrease in temperature. Number of charge carriers available for conduction increase with increase in temperature and its conductivity increases. The resistivity of superconductors decreases with decrease in temperature and below a certain temperature called critical temperature it becomes zero. This certain temperature is different for different superconducting materials.

Two resistances are to be connected in which combination so that the equivalent resistance becomes less than the individual resistances?

The resistances must be connected in parallel combination. When two more resistances are connected in parallel, the equivalent resistance is the smaller than the smallest one. For example, the equivalent resistance of 2 Ω , 3 Ω and 4 Ω will be smaller than the 2 Ω resistance which is the smallest of the three given resistances.

What is meant by electrical power? The rating of a bulb is written as 220 V - 100 W . What is its meaning?

Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. It is the rate of doing work. Its SI unit is watt. It is equivalent to one joule per second. Power of the given bulb is 100 W and, the supply voltage is 220 V . The given rating of the bulb means that it dissipates 100 J of energy per second when connected to a potential difference of 220 V . Hence, the bulb can be connected to the maximum voltage of 220 volts and it can consume the maximum power of 100 watts.

The series combination of two 10 ohm resistances is connected in parallel combination with a 20 ohm resistance. Determine the equivalent resistance of the final combination.

The equivalent resistance of the series combination of two 10 ohm resistances: R s = 10 + 10 Ω = 20 Ω When it is connected in parallel to another 20 Ω resistance, the equivalent resistance will be: 1 R = 1 20 + 1 20 ⇒ R = 10 Ω The equivalent resistance of the final combination will be 10 Ω .

Two metallic conductors A and B of same lengths have resistivities of 1 . 6 × 10 - 8 Ωm and 3 . 2 × 10 - 8 Ωm respectively. These two conductors are separately connected to the same potential difference. What should be the ratio of their cross-sections in order to have the same current flowing through each of them?

Resistance of a conductor of length L, area of cross-section A and the resistivity ρ is written as: R = ρ L A Hence, for two wires of same length: R 1 = 1 . 6 × 10 - 8 × L A 1 R 2 = 3 . 2 × 10 - 8 × L A 2 If they are connected across the same potential difference and the same current flows through them: V = I R 1 = I R 2 ⇒ 1 . 6 × 10 - 8 × L A 1 = 3 . 2 × 10 - 8 × L A 2 ⇒ A 1 A 2 = 1 2 The ratio of their cross-section will be 1 : 2 .

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 6 - Current Electricity>West Bengal Board-2019>Q 14

MEDIUM

10th West Bengal Board

IMPORTANT

Earn 100

A thin wire and a thick wire of the same conducting material have the same length. Which one of them will carry more current when connected to the same potential difference?

Important Questions on Current Electricity

MEDIUM

10th West Bengal Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 6 - Current Electricity>West Bengal Board-2019>Q 15

Two resistance $r_{1} and r_{2}$ when connected separately to the same potential difference, it was seen that the current flowing through $r_{1}$ was six times the current flowing through $r_{2}$ . Determine the ratio of $r_{1}$ and $r_{2}$ .

MEDIUM

10th West Bengal Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 6 - Current Electricity>West Bengal Board-2019>Q 16

A current of $1 A$ flows when an electric bulb is connected to $220 V$ mains. What would be the current when the same bulb is connected to a $110 V$ main?

MEDIUM

10th West Bengal Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 6 - Current Electricity>West Bengal Board-2019>Q 17

Find the ratio of resistances for two bulbs of $220 V - 60 W and 110 V - 60 W$ .