CBSE Class 10 Science Electricity Assignment Set C

Question : Which of the following terms does not represent electrical power in a circuit?
a. I²R
b. IR²
c. VI
d. V²/ R

Answer : B

 

Very Short Answers :

Question : Name a device that helps to maintain a potential difference across a conductor.
Answer : Cell or battery

Question : Two resistors of 10 Ω and 15 Ω are connected in series to a battery of 6 V. How can the values of current passing through them be compared?
Answer :  In series, same current flows through each resistor. So, ratio of current is 1: 1.

Question. What is meant by saying that the potential difference between two points is 1 V? 
Answer: The potential difference between two points is said to be 1 volt if 1 joule of work is done in moving 1 coulomb of electric charge from one point to the other.

Question. Calculate the least count of voltmeter in which there are 10 divisions between 1.0 V and 1.5 V marks.
Answer: Least count = 0.5/10 = 0.05.

Question. Would you connect a fuse in series or in parallel to an electric circuit ?
Answer: In series, of the electric circuit before appliances are present in the circuit.

Question. Why do electricians wear rubber hand gloves while working ?
Answer: Rubber is an electrical insulator. Hence, electrician can work safely while working on an electric circuit without a risk of getting any electric shock.

Question. An electric heater is rated ‘1500 W, 250 V’. The heater is connected to 250 V mains. Calculate :
(a) The current drawn.
(b) The energy consumed in 50 hours.
(c) The cost of energy consumed at ₹6 per kWh.
Answer: (a) 6A, (b) 75 kWh, (c) Rs. 450.

Question. Which substance is used for making resistance coil of electric heater and why ?
Answer: Nichrome, due to its high resistivity.

Question. What is commercial units of electrical energy ? Convert it into joules.
Answer: The commercial unit of electrical energy is kWh.
1 kWh = 1000 W × 1 hour
= 1000 J/s × 60 × 60 s
= 3.6 × 106 J

Question. Name and define the S.I. unit of electric power.
Answer: The S.I. unit of electric power is watt (W). One watt is the power consumed by an electrical device when it is operated at a potential difference of one volt and carries a current of one ampere.
1 watt = 1 volt × 1 ampere.

Question. Why is an ammeter connected in series in an electric circuit ?
Answer: It is connected in series so that whole of electric current, which it has to measure, passes through it.

Question. A boy noted the readings of his home’s electricity meter on 1st June and again on 1st July (as shown in figure given below) :
(a) What was the meter reading on 1st June ?
(b) What was the meter reading on 1st July ?
(c) How many units of electrical energy have been used ?
(d) Calculate the cost of electrical energy used, if the rate is Rs.
5 per unit.
Answer: (a) 67602
(b) 67912
(c) 310
(d) Rs. 1550.

Question. In an activity performed by a girl to estimate the monthly bill of her house, she reported that 3 bulbs of 100 W each, 2 fans of 50 W each and 1 T.V. set of 60 W are used daily for an average of 8 hours, 10 hours and 5 hours respectively.
(a) Calculate the electrical energy (in kWh) consumed in 1 month.
(b) If the cost of electrical energy is R 6 per unit, what is the monthly bill ?
Answer: (a) 111 kWh
(b) ₹ 666.

Question. Is Joule heating always desirable ?
Answer: No.

Question. Write the function of voltmeter in an electric circuit.
Answer: Voltmeter measures the potential difference across in a circuit. It is always connected in parallel in the circuit.

Question. Write two points of difference between electrical energy and electric power.
Answer: 

Given,

current ( i ) = 2 A

voltage ( v ) = 4 V

Resistance of bulb is R1 = 8Ω

resistance ( R ) = ?

 

 

Question :  Radhika is a student of class X. Her mother was making tea in an old electric kettle having metal case. When she switched on the power supply to the electric kettle. She got a severe electric shock. Radhika put off the main switch quickly and found that the connecting cord was torn, where her mother touched the metal case of the kettle.

She also found that the red and black wires of connecting cord were firmly connected to the two lower terminals of the power plug but the green wire of cord was not connected to the upper terminal of the plug. Radhika replaced the torn connecting cord and also connected to the three wires of cord firmly to the power plug terminals.

On the basis of the above passage, answer the following questions: 

i. Why did Radhika put off the main switch quickly?

ii. Which wire red, black or green, touched the metal case of electric kettle when Radhika's mother got electric shock?

iii. What values are displayed by Radhika in this incident?

Answer :

i. Radhika put off the main switch quickly to save her mother.

ii. Red wire which is at a high potential of  220V was touching the metal case of electric kettle.

iii. The values displayed by Radhika are:

a. Concern for her mother.

b. Presence of mind.

c. Knowledge of household wiring and daily life activities.  

Question : What would you suggest to a student if  while performing an experiment he finds that the pointer hneedle of the ammeter and voltmeter do not coincide with the zero marks on the scales when circuit is open? No extra ammeter  voltmeter is available in the laboratory. 
Answer :  As pointer of both the ammeter and voltmeter do not coincide with the zero marks on the scales when circuit is open, it indicates zero error in both the instruments. This zero error should be subtracted from the readings taken when circuit is closed. o get correct readings using these instruments, first we should find out the Least counts of both the nstruments, i.e., the minimum value which can be accurately measured.
Zero error = Initial reading (in open circuit) = Pointer reading (in open circuit) X Least count To get the actual reading, subtract zero error or the initial reading of the open circuit to the reading when you perform the experiment. Actual reading = Final reading - Initial reading

Long Answers :

If 1V potential difference is there and 1A current is flowing then it is said that there is 1 ohm resistance.

 

 

Thus, resistance will decrease by four times, if radius of wire is doubled.

Question : (A) Define electrical energy with S.I. unit?
(B) A household uses the following electric appliance;
(i) Refrigerator of rating 400w for ten hour each day.
(ii) Two electric fans of rating 80w each for twelve hours each day.
(iii) Six electric tubes of rating 15w each for six hours each day.
Calculate the electricity bill of the household for the month of june if the cost per unit of electric energy is ` 3.00.
Answer :  (A) The work done by a source of electricity to maintain current in a circuit is known as electrical energy. Its S.I. unit is Joule.
(B) (i) Electricity consumed by refrigerator = Power × Time
                                                              = 400 × 10
                                                              = 4000 Wh
                                                              = 4 kWh
(ii) Electricity consumed by two fans
                                                              = Power × Time
                                                              = 80 × 2 × 12
                                                              = 1920 Wh
                                                              = 1.92 kWh
(iii) Electricity consumed by six electric tubes
                                                              = 6 × 18 × 6
                                                              = 648 Wh
                                                              = 0.648 kWh
Total energy consumed in one day
                                                              = 4 + 1.92 + 0.648
                                                              = 6.548 kWh
Total energy consumed in one month
                                                              = 6.548 × 30
                                                              = 197.04 kWh
Cost of 1 unit (kWh)                                 = R 3.00
Cost of 197.04 kWh                                  = 197.04 × 3.00
Total electricity bill                                    = R 591.12

Question : How much current will an electric bulb draw from 220 V source if the resistance of the bulb is 1200Ω? If in place of bulb, a heater of resistance 100 Ω is connected to the sources, calculate the current drawn by it.
Answer : 

Question : Out of the two wires X and Y shown below, which one has greater resistance? Justify your answer.

Answer :  Wire ‘Y’ has greater resistance as it has more length than wire ‘X’. It is because resistance of wire is directly proportional to the length of wire. 

Question : The figure below shows three cylindrical copper conductors along with their face areas and lengths. Discuss in which geometrical shape the resistance will be highest.

Answer :

Question : Two wires A and B are of equal length and have equal resistance. If the resistivity of A is more than that of B, which wire is thicker and why? For the electric circuit given below calculate:

(i) Current in each resistor,
(ii) Total current drawn from the battery, and
(iii) Equivalent resistance of the Circuit
Answer :

So, for different materials having same resistance per unit length, greater resistivity material wire has more cross-sectional area.
Hence, wire A is thicker than that of B.
(i) Current through each resistor