Science · Effects of current · chapter 11 of 13

Class 10 Science Chapter 11: Electricity case study question with answers

One case-based question of the kind the board asks in Section E: a passage and a table, then 3 parts worth 4 marks in all, with the answer and the marking scheme for each. Written from the NCERT chapter.

Case study · 4 marks

The Nair family in Thrissur want to understand their electricity bill. For one typical day they note the power rating of each appliance in their flat and how long it runs. The supply is 230 V, and the electricity board charges ₹6 for each unit of energy. Their brother says the iron must use the most energy because it has the highest rating; their mother thinks the fan, which runs most of the day, may use more.

Appliance	Power (W)	Use per day (h)
Ceiling fan	75	8
LED television	100	4
Mixer	500	0.4
Electric iron	1000	0.5

Part 1 · 1 mark

Which appliance consumes the most electrical energy in a day?

(a) ceiling fan(b) electric iron(c) mixer(d) LED television

Show answer

Answer: (a) ceiling fan

Energy = power × time: fan 75 × 8 = 600 W h, iron 1000 × 0.5 = 500 W h, television 400 W h, mixer 200 W h. The fan uses the most though its rating is low.

Part 2 · 1 mark

The total electrical energy consumed by the four appliances in a day is

(a) 6.12 MJ(b) 1.7 MJ(c) 0.47 MJ(d) 61.2 MJ

Show answer

Answer: (a) 6.12 MJ

600 + 400 + 200 + 500 = 1700 W h = 1.7 kW h; 1.7 × 3.6 × 10⁶ J = 6.12 × 10⁶ J = 6.12 MJ.

Part 3 · 2 marks

Find the family's bill for these appliances for 30 such days.

Answer and marking scheme

1.7 kW h a day × 30 = 51 kW h = 51 units. Bill = 51 × ₹6 = ₹306.

51 units in 30 days (1)
bill ₹306 (1)

Find the current drawn by the iron and choose its fuse from 2 A, 5 A and 10 A.

Answer and marking scheme

I = P/V = 1000/230 ≈ 4.35 A. The fuse is the next rating above the working current: 5 A.

I = P/V ≈ 4.35 A (1)
5 A fuse (1)

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