(a) Which of the two, alternating current or direct current, produces a varying magnetic field when it flows through a conductor? (b) State the frequency of the alternating current supply in India.

A copper rod PQ carrying current is kept in a magnetic field as shown in the diagram. (a) The copper rod PQ will move towards C. State True or False. (b) Name the law used to determine the direction of motion of PQ. (c) What will be the effect on the force experienced if rod PQ is replaced by another copper rod of the same length but greater cross-sectional area? (d) Justify your answer in (c).

Complete the following by choosing the correct answers from the bracket: (a) In uniform circular motion the centrifugal force acts ............... [towards the centre/away from the centre/along the tangential direction]. (b) Refractive index of a medium is independent of ............... [temperature/angle of incidence/wavelength of light]. (c) Heat absorbed during change of phase depends on ............... [mass/change in temperature/specific heat capacity] of the substance. (d) Emf of a cell is ............... [greater than/less than/equal to] the terminal voltage when the cell is in open circuit. (e) In a step-up transformer the turns ratio is ............... [more than 1/less than 1/equal to 1]. (f) The nuclear radiation with lowest ionising power is ............... [α/β/γ].

The following figure shows a small bar magnet falling freely through a copper ring. For the observer at A, the direction of the induced current will be : (a) clockwise when magnet is above and below the ring (b) anticlockwise when magnet is above and below the ring (c) anticlockwise when magnet is above the ring and clockwise when the magnet is below the ring (d) clockwise when magnet is above the ring and anticlockwise when the magnet is below the ring

A copper conductor is placed over two stretched copper wires whose ends are connected to a D.C. supply as shown in the diagram. (a) What should be the magnetic poles at the points A and B lying on either side of the conductor to experience the force in the upward direction? (b) Name the law used to find these polarities.

State two factors affecting the speed of rotation of the coil in a D.C. motor.

In an AC generator, name the part which has the following functions: (a) intensifies the magnetic field. (b) maintains electrical contact between the rotating parts and the external circuit.

The diagram below shows a cardboard on which iron filings are kept. A wire bent in the form of a loop is seen passing through the cardboard. When current flows through it the iron filings arrange themselves as shown below. (a) State the polarities of the battery at A and B. (b) State the effect on the magnetic field if an iron rod is held along the axis of the coil. (c) State one way to: (1) Change the polarity of the coil. (2) Decrease the strength of the magnetic field around the coil.

If the strength of the current flowing through a wire is increased, the strength of the magnetic field produced by it: (a) decreases (b) increases (c) remains the same (d) first increases then decreases

(a) State one factor that affects the magnitude of induced current in an AC generator. (b) Given below is a circuit to study the magnetic effect of electric current. ABCD is a cardboard kept perpendicular to the conductor XY. A magnetic compass is placed at the point P of the cardboard. P1 and P2 are the positions of the magnetic compass, before and after passing a current through XY respectively. (i) Name the rule that is used to predict the direction of deflection of the magnetic compass. (ii) State the direction of current in the conductor (X to Y or Y to X) when the circuit is complete. (iii) If resistance R is increased, then what will be the effect on the magnetic lines of force around the conductor?

Below is the diagram of a transformer: (a) Identify the type of transformer. (b) In this type of transformer which of the wire is thicker, the primary or the secondary? Give a reason.

When the magnet shown in the diagram is moved towards the coil at a speed of 5 m s−1, the galvanometer shows a certain deflection to the right. How will the direction and magnitude of deflection change when the coil also moves with a speed of 5 m s−1: (a) in the direction of motion of the magnet? (b) in the opposite direction to the motion of the magnet?