# Electricity

## Solution of Intext Questions (NCERT Book)- Part-2

Question: 14:- Judge the equivalent resistance when the following are connected in parallel (a) 1 Ω and 106 Ω, (b) 1 Ω and 103 Ω, and 106 Ω.

Question: 15:- An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source.

What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?

Given:

R1 = 100Ω, R2 = 50 Ω, R3 = 500 Ω all are connected in parallel

Potential difference = 220V

For electric iron

Since it takes as well current as three appliances, thus electric current through it = 7.04A

The electric current = 7.04 A and potential difference = 220 V

Thus, Resistance of electric iron = Total resistance of three appliances = 31.25 Ω

Thus, electric current through the electric iron = 7.04A

Resistance of electric iron = 31.25 Ω

Question: 16:- What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?

(a) Voltage remains same in all the appliances.

(b) Lower total effective resistance

Question: 17. How can three resistors of resistances 2 Ω, 3 Ω, and 6 Ω be connected to give a total resistance of (a) 4 Ω, (b) 1 Ω?

(a) When resistors having resistance equal to 3 Ω and 6 Ω are connected in parallel and one having resistance equal to 2 Ω is connected in series

Let total resistance due to resistors having resistance equal to 6 Ω and 3 Ω = R1

Now, total effective resistance in the circuit = R1 + 2 Ω = 2 Ω + 2 Ω = 4 Ω

Hence, when resistors having resistance equal to 3 Ω and 6 Ω are connected in parallel and one having resistance equal to 2 Ω is connected in series, then the total effective resistance in the circuit = 4 Ω

(b) When all the three resistance is connected in parallel then

When all the three resistance will be connected in parallel, then the total effective resistance in the circuit = 1 Ω

Question: 18. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?

Answer: When all the resistors are connected in series

Thus, R = 2 Ω

(b) When all the resistors are connected in series

Thus, total resistance = 4 Ω + 8 Ω + 12 Ω + 24 Ω = 48 Ω

Thus, highest resistance = 48 Ω

Lowest resistance = 2 Ω

Page Number 218

Question: 19. Why does the cord of an electric heater not glow while the heating element does?

The resistance of heating element is very high compared to the cord of an electric heater. Since, heat produced is directly proportional to the resistance, thus element of electric heater glows because of production of more heat and cord does not.

Question: 20. Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.

Given, Potential difference (V) = 50V,

Charge (Q) = 96000 coulomb

Time, t = 1 hour = 60 X 60 s = 3600 s

Heat produced =?

Question: 21. An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.

Given, Electric current (I) = 5A, Resistance (R) = 20 Ω, Time (t) = 30s

Therefore, Heat produced (H) =?

Question: 22. What determines the rate at which energy is delivered by a current?

Answer: Since electric power is the rate of consumption of electric energy in any electrical appliance. Hence, rate at which energy is delivered by a current is the power of electric appliance.

Question: 23. An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.