CBSE Class 10 Science 2020 · Paper 31/4/1 · Question 30

(a) Fleming’s left-hand rule: stretch the thumb, forefinger and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, then the thumb points in the direction of the motion of the conductor, that is, of the force acting on it. (b) The current used in our homes is alternating current, which reverses its direction periodically; its frequency is $50$ Hz; and the potential difference between the live wire and the neutral wire is about $220$ V. (c) A fuse is a safety device: a short piece of wire of low melting point connected in series in the live wire of a circuit or appliance. It is called a safety device because, when an unduly high current flows through it because of overloading or short-circuiting, the heat produced ($H=I^{2}Rt$) melts the fuse wire and breaks the circuit, stopping the current and preventing damage to the circuit and the appliances. (d) Earthing joins the metallic body of the appliance to the earth through a low-resistance conducting path. If current leaks to the body, it flows to the earth through this path and the body stays at the earth's potential, so the user is protected from a severe electric shock.