Karnataka SSLC 10th Science Question Paper 2021

An electric generator works on the principle of electromagnetic induction (Faraday's law), where mechanical energy is converted into electrical energy by rotating a coil in a magnetic field. An electric motor (c) and fan (d) typically use the magnetic effect of current to produce motion, and an electric heater (b) works on the heating effect of electric current.

In a series circuit, the total resistance $R_{total} = R_1 + R_2$. Given $R_1 = 30 \, \Omega$ and $R_2 = 6 \, \Omega$, $R_{total} = 30 + 6 = 36 \, \Omega$. Using Ohm's Law $V = I \cdot R$, the current $I = V / R_{total} = 9 \text{ V} / 36 \, \Omega = 0.25 \text{ A}$.

Black surfaces are excellent absorbers of heat radiation. Painting the inner wall of a solar cooker black ensures that the solar energy falling on it is absorbed efficiently to cook the food inside, rather than being reflected (a).

Tungsten is used for the filament of an electric bulb because it has a very high melting point ($3380^\circ \text{C}$), allowing it to glow at high temperatures without melting, and it does not oxidize readily.

In a DC generator (or simple rotating coil), the current changes direction every half revolution as the sides of the coil swap positions relative to the magnetic poles, which is why a split-ring commutator is often used to ensure unidirectional output.