Refraction / Optics - Properties of Light : 3
Q. Total resistance of resistors in parallel is -
Ans - Less than each individual resistance
Explanation: Parallel connection provides multiple current paths; combined conductance increases, so equivalent resistance is always smaller than the smallest branch resistance.
Q. Two 1 Ω resistors connected in parallel: equivalent resistance = ?
Ans - 0.5 Ω
Explanation: For two identical resistors R in parallel, Req = R/2. So with R = 1 Ω, Req = 0.5 Ω, halving the single-resistor value.
Q. Two/three resistances in series example (sum = 302 Ω)
Ans – 302 Ω (assuming resistances 10, 12, 280 Ω)
Explanation: In series, equivalent resistance equals the arithmetic sum of individual resistances. For assumed values 10 + 12 + 280 = 302 Ω (series addition).
Q. When current is drawn from a cell, terminal potential difference is -
Ans - Less than its emf
Explanation: Internal resistance inside a cell causes a voltage drop when current flows; terminal voltage = emf − I·internal resistance, so it falls below the open-circuit emf.
Q. Value of 1 joule in calories ?
Ans - ≈ 0.24 calorie
Explanation: One joule equals about 0.239006 calories (small-c calorie), often approximated as 0.24 cal; conversion: 1 cal ≈ 4.186 J.
Q. SI unit of energy ?
Ans - Joule (J)
Explanation: The joule is the SI unit of energy, work, and heat—one joule equals one newton-meter of work or energy transferred when applying one newton through one metre.
Q. Which effect of electric current does an electric heater use ?
Ans - Thermal (heating) effect
Explanation: Electric heaters convert electrical energy to heat via Joule heating (I²R losses) in resistive elements, warming surroundings through conduction, convection, and radiation.
Q. Material used for electric heater coils ?
Ans - Nichrome
Explanation: Nichrome (nickel-chromium alloy) resists oxidation and has stable resistivity at high temperatures, making it ideal for durable, high-temperature heating elements.
Q. The property of a circuit that converts electrical energy into heat is -
Ans - Resistance
Explanation: Resistance causes electrical energy to dissipate as heat when current flows (Joule heating). Higher resistance for given current yields greater rate of heat production (P = I²R).