QQuestion
Two metallic wires A and B of the same length are made of the same material. The radius of wire A is double the radius of wire B. What is the ratio of resistances of the two wires? [3]
OR
There are three 220V-60W electric lamps and two 220V-100W electric fans in the house. The electric lamps are lit for 5 hours a day and the fans are run for 10 hours a day. If the cost per B.O.T unit is Rupees 5, what will be the cost of electricity for 30 days? [3]
✓Answer
R = ρ {l}\over {a}
or,R = ρ {l}\over πr^2
⇒ R ∝ 1\over r^2
⇒ {R_A} \over {R_B} = {{r_B}^2\over {r_A}^2
Given: rA = 2rB
⇒ R_A\over R_B = {{r_B}^2\over {2r_B}^2
⇒ R_A\over R_B = {{r_B}^2\over 4{r_B}^2
⇒ R_A\over R_B = 1\over 4
∴ The ratio of resistances of the two wires 1 : 4.
OR
Energy Consumption of the Lamps
- Power of each lamp = 60 W
- Total power for 3 lamps = 3 × 60 W = 180 W
- Daily energy consumption = 180 × 5 hours = 900Wh
Energy Consumption of the Fans
- Power of each fan = 100 W
- Total power for 2 fans = 2 × 100 W = 200 W
- Daily energy consumption = 200 W × 10 hours = 2000 Wh
Total Energy Consumption per Day
= 900Wh + 2000 Wh
= 2900 Wh
= 2.9 kWh
Total Energy Consumption (30 Day) = 2.9 kWh × 30
= 87 kWh
Total cost = ₹ 5 × 87 = ₹ 435
Related Questions
More WBBSE Hard level questions
The equivalent resistances of two conductors are 9 Ω and 2 Ω when they are connected in series and parallel combinations respectively. Find the resistances of those two conductors. OR Find the equivalent resistance between A and B points of the following circuit.
If two electric bulbs of ratings ‘240V-60 W’ and ‘240V-100W’ are connected in series, which one will shine brighter? (Filaments of both the bulbs are of the same material).[3] OR An electric cell of internal resistance 5 Ω and emf 2 V is connected to a resistor of 15 Ω. Determine the potential difference between the two ends of the cell. [3]
Write Faraday's laws of electromagnetic induction. Mention one advantage of using a LED lamp over an incandescent lamp. [2 + 1]
Three equal resistors connected in series across a source of e.m.f. together dissipate 10 W of power. What would be the power dissipated if the same resistors were connected in parallel across the same source of e.m.f.?
When two conductors are connected in series, the equivalent resistance is 25 Ω, and when connected in parallel, the equivalent resistance is 6 Ω. Determine the resistance of each conductor.
What is the importance of insulators in household wiring?
What is DC?
Write one characteristic of each of electrical heater wire and fuse wire. [1 + 1]
If the same potential difference is applied between the two ends of iron and copper wires having the same length and cross section, does equal amount of current flow through the two wires?
If a current of 0.2 ampere flows through a conductor of resistance 40 ohm, what is the potential difference between the two ends of the conductor? 0.5 volt 2 volt 6 volt 8 volt
Write down the difference between dynamo and electric motor. What is earthing?
State Ohm's law. If a potential difference of 10 V is applied between the two ends of a conductor, an electric current of 0.1 A flows. Determine the resistance of the conductor. [2 + 1]