CBSE Class 10 Science Chapter 13: Magnetic Effects of Electric Current NCERT Solutions

The correct description of the magnetic field near a long straight wire carrying current is that it consists of concentric circles centered on the wire. This can be determined by applying the right-hand thumb rule. Imagine holding the wire with your right thumb pointing in the direction of the current; your fingers will curl around the wire in the direction of the magnetic field lines, which are observed to be circular and centered on the wire.

Therefore, option (d) is correct.

Electromagnetic induction is the process by which a current is produced in a conductor when it is exposed to a changing magnetic field. This change in the magnetic field can be achieved by moving a magnet near a coil of wire or by changing the current in a nearby coil. The relative motion between the magnet and the coil is crucial for inducing a current.

Therefore, option (c) accurately describes electromagnetic induction.

A generator is a device that converts mechanical energy into electrical energy. It works on the principle of electromagnetic induction to produce electric current. A galvanometer detects current, an ammeter measures current, and a motor converts electrical energy into mechanical energy.

Hence, the correct option is (a) generator.

The fundamental difference between an AC generator and a DC generator lies in the mechanism used to connect the rotating coil to the external circuit. An AC generator uses slip rings, which are continuous rings that allow the alternating current generated in the coil to flow into the external circuit without changing its direction relative to the external circuit. In contrast, a DC generator uses a commutator, which is a split ring that reverses the connection to the external circuit every half rotation of the coil. This reversal ensures that the current in the external circuit always flows in the same direction, producing direct current.

Therefore, option (d) correctly identifies this essential difference.

A short circuit occurs when the live wire and the neutral wire of an electrical circuit come into direct contact, often due to damaged insulation. This direct contact bypasses the normal load (like appliances) and creates a path of very low resistance. According to Ohm's law ($V\; =\; IR$), if the resistance ($R$) decreases significantly while the voltage ($V$) remains nearly constant, the current ($I$) must increase dramatically. This heavy surge of current can cause overheating and is a fire hazard, which is why fuses or circuit breakers are used to interrupt the circuit.

Hence, option (c) is correct.