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This is a foundational chapter on electricity. Focus on Ohm's law ($V = IR$), the factors affecting resistance ($R = \rho \frac{L}{A}$), and the heating effect of current ($H = I^2Rt$). Understand the difference between…
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Derive the expression for the equivalent resistance of three resistors connected in series.
$R_{eq} = R_1 + R_2 + R_3$.
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Derive the expression for the equivalent resistance of three resistors connected in parallel.
$1/R_{eq} = 1/R_1 + 1/R_2 + 1/R_3$.
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A house has 5 bulbs of 60 W each used for 4 hours daily, and a heater of 1500 W used for 2 hours daily. Calculate the energy consumed in a month of 30 days and the cost at ₹5 per unit.
Energy = 126 kWh; Cost = ₹630.
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An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, what will be the power consumed?
25 W (since $P \propto V^2$).
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Explain the working of an electric fuse and why it is connected in series with the live wire.
Fuse melts on overcurrent, breaking the circuit; series connection ensures all current passes through it.
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Describe an experiment to verify Ohm's law. Include circuit diagram and the V-I graph.
Connect a resistor, ammeter, voltmeter and rheostat in a circuit; vary voltage and plot V vs I to get a straight line.
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An electric iron draws a current of 5 A from a 220 V supply. Calculate the power of the iron and the energy consumed in 2 hours.
Power = 1100 W; Energy = 2.2 kWh.
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Explain the heating effect of electric current and give two applications.
When current flows through a resistor, electrical energy is converted into heat; used in electric heaters, irons, and bulbs.
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A wire of resistance 10 Ω is bent to form a closed circle. Find the resistance between two diametrically opposite points.
2.5 Ω (two 5 Ω resistors in parallel).
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Explain the factors affecting resistance of a conductor and derive the relation $R = \rho \frac{L}{A}$.
Resistance is directly proportional to length and inversely proportional to area, with proportionality constant resistivity.
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Differentiate between series and parallel combination of resistors.
In series, current is same and voltage divides; in parallel, voltage is same and current divides.
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State the law of combination of resistances in series and parallel.
Series: $R_{eq} = R_1 + R_2 + ...$; Parallel: $1/R_{eq} = 1/R_1 + 1/R_2 + ...$
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Define electric current and state its SI unit.
Electric current is the rate of flow of electric charge, measured in amperes (A).
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State Ohm's law.
At constant temperature, the current through a conductor is directly proportional to the potential difference across its ends.
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Define resistance and state its SI unit.
Resistance is the opposition offered by a conductor to the flow of current, measured in ohms (Ω).
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State the factors on which the resistance of a conductor depends.
Resistance depends on length, cross-sectional area, material (resistivity), and temperature.
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Define electric power and state its SI unit.
Electric power is the rate at which electrical energy is consumed or produced, measured in watts (W).
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State Joule's law of heating.
Heat produced in a conductor is directly proportional to the square of current, resistance, and time of flow.
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What is the commercial unit of electrical energy? Define it.
The commercial unit is the kilowatt-hour (kWh), which is the energy consumed by a 1 kW appliance in 1 hour.
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What is the function of an electric fuse?
An electric fuse protects the circuit from overloading and short-circuiting by melting when current exceeds a safe limit.
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Why is earthing necessary in domestic electrical circuits?
Earthing prevents electric shocks by providing a low-resistance path for leakage current to flow to the ground.
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What is the SI unit of resistivity?
Ohm-meter (Ω m).
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