Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current carrying loop is brought near it? Describe some salient features of magnetic lines of field concept.
A magnetic compass needle aligns itself along the earth’s magnetic field in the absence of any other magnetic influence. When a bar magnet or a current-carrying loop is brought near it, the magnetic field created by them interacts with the earth’s magnetic field. This modifies the net magnetic field at the position of the compass and causes the needle to deflect.
Magnetic field lines emerge from the North pole and enter the South pole. They represent both the direction and the magnitude of the magnetic field. The magnetic field strength is indicated by the closeness of field lines. Field lines never cross each other because two different magnetic field directions cannot exist at the same point. If field lines are parallel and equispaced in a region, the magnetic field is considered uniform.
With the help of a labelled circuit diagram illustrate the pattern of field lines of the magnetic field around a current carrying straight long conducting wire. How is the right hand thumb rule useful to find direction of magnetic field associated with a current carrying conductor?
The magnetic field around a current-carrying straight conductor consists of concentric circles centred on the wire. The direction of the magnetic field depends on the direction of current in the conductor.
According to the right-hand thumb rule, if the current-carrying conductor is held in the right hand such that the thumb points in the direction of current, then the fingers curled around the conductor give the direction of magnetic field lines. This rule helps determine the orientation of the circular field around the straight conductor.
Explain with the help of a labelled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current carrying coil has \( n \) turns the field produced at any point is \( n \) times as large as that produced by a single turn?
The magnetic field produced by a current-carrying circular loop appears as concentric circles near the wire and becomes nearly straight near the centre of the loop. The field is strongest at the centre of the loop.
If there are \( n \) turns in the circular coil, each turn carries the same current and produces a magnetic field of the same magnitude at the centre. These individual fields add up in the same direction. Therefore, the total magnetic field at the centre becomes \( n \) times the magnetic field produced by a single turn.
Describe the activity that shows that a current-carrying conductor experiences a force perpendicular to its length and the external magnetic field. How does Fleming's left-hand rule help us to find the direction of the force acting on the current carrying conductor?
When a current-carrying conductor is placed in a region of an external magnetic field, it experiences a force. This can be demonstrated by suspending a current-carrying wire between the poles of a magnet. When current flows through the wire, the conductor is seen to move, showing that a force acts on it. When the direction of current is reversed, the direction of motion is also reversed, confirming the dependence on current direction.
Fleming’s left-hand rule states that if the thumb, forefinger, and middle finger of the left hand are stretched mutually perpendicular, the forefinger represents the direction of magnetic field, the middle finger represents the direction of current, and the thumb gives the direction of force or motion. This helps determine the direction of force on the conductor.
Draw a labelled circuit diagram of a simple electric motor and explain its working. In what way are simple electric motors different from commercial motors?
A simple electric motor works on the principle that a current-carrying coil in a magnetic field experiences a torque that rotates the coil. When current flows through the rectangular coil placed between two magnetic poles, opposite forces act on the two sides of the coil, producing rotation. A split-ring commutator reverses the direction of current in the coil every half-turn, ensuring continuous rotation in the same direction.
Commercial motors differ in that they use an electromagnet instead of a permanent magnet, have many turns of conducting wire in the coil to increase force, and use a soft iron core on which the coil is wound to enhance the magnetic effect.
Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.
Electromagnetic induction is the process by which a change in magnetic field linked with a closed conductor induces an electric current in it. The induced current arises due to the changing magnetic flux through the loop.
To demonstrate this, take two coils wound on a soft iron core. Connect one coil to a battery and a switch, and the other coil to a galvanometer. When the switch of the first coil is closed or opened, the galvanometer in the second coil shows a momentary deflection, indicating that a current is induced whenever the magnetic field through the second coil changes. Increasing or decreasing current in the primary coil similarly induces current in the secondary coil.
Describe the working of an AC generator with the help of a labelled circuit diagram. What changes must be made in the arrangement to convert it to a DC generator?
An AC generator works on the principle of electromagnetic induction. A coil is rotated in a magnetic field, causing the magnetic flux through the coil to change continuously. This produces an alternating induced emf in the coil. Slip rings attached to the coil allow the alternating current to be taken out through brushes.
To convert an AC generator into a DC generator, the slip rings must be replaced with a split-ring commutator. This ensures that the direction of current in the external circuit remains the same, producing direct current instead of alternating current.
Draw an appropriate schematic diagram showing common domestic circuits and discuss the importance of fuse. Why is it that a burnt out fuse should be replaced by another fuse of identical rating?
Domestic wiring consists of live, neutral, and earth wires connected to various household devices through switches and distribution circuits. Fuses are included in the live wire to protect appliances from overloading or short-circuiting.
A fuse melts when excessive current flows, thereby breaking the circuit and preventing damage. A burnt-out fuse must be replaced with one of the same rating because a fuse with a higher rating may not blow when needed, potentially damaging appliances.