Section – B
A square sheet of side ‘a’ is lying parallel to XY plane at z = a. The electric field in the region is . The electric flux through the sheet is
Three charges q, –q and q0 are placed as shown in figure. The magnitude of the net force on the charge q0 at point O is
A + 3.0 nC charge Q is initially at rest at a distance of r1 = 10 cm from a + 5.0 nC charge q fixed at the origin. The charge Q is moved away from q to a new position at r2 = 15 cm. In this process work done by the field is
- 1.29 x 10-5 J
- 3.6 x 105 J
- -4.5 x 10-7 J
- 4.5 x 10-7 J
A car battery is charged by a 12 V supply, and energy stored in it is 7.20 x 105 J. The charge passed through the battery is –
- 6.0 x 104 C
- 5.8 x 103 J
- 8.64 x 106 J
- 1.6 x 106 C
A straight conducting rod of length l and mass m is suspended in a horizontal plane
by a pair of flexible strings in a magnetic field of magnitude B. To remove the tension
in the supporting strings, the magnitude of the current in the wire is
A constant current is flowing through a solenoid. An iron rod is inserted in the solenoid along its axis. Which of the following quantities will not increase?
- The magnetic field at the centre
- The magnetic flux linked with the solenoid
- The rate of heating
- The self-inductance of the solenoid
A circuit is connected to an AC source of variable frequency. As the frequency of the source is increased, the current first increases and then decreases. Which of the following combinations of elements is likely to comprise the circuit?
- L, C and R
- L and C
- L and R
- R and C
If n, e, and m have their usual meanings, then the resistance of a wire of length l and cross-sectional area A is given by -
A proton and an alpha particle move in circular orbits in a uniform magnetic field. Their speeds are in the ratio of 9:4. The ratio of radii of their circular orbits is
A coil of area 100 cm2 is kept at an angle of 30° with a magnetic field of 10-1 T. The magnetic field is reduced to zero in 10-4. The induced emf in the coil is -
- 5.0 V
- 50.0 V
A 15 resistor, an 80 mH inductor and a capacitor of capacitance C are connected in series with a 50 Hz AC source. If the source voltage and current in the circuit are in phase, then the value of capacitance is
Four objects W, X, Y and Z, each with charge +q are held fixed at four points of a square of side d as shown in the figure. Objects X and Z are on the midpoints of the sides of the square. The electrostatic force exerted by object W on object X is F. Then the magnitude of the force exerted by object W on Z is
Two sources of equal emf are connected in series. This combination is, in turn connected to an external resistance R. The internal resistance of two sources are r1 and r2 (r2 > r1). If the potential difference across the source of internal resistance r2 is zero, then R equals to-
Which of the following statements is correct?
- Magnetic field lines do not form closed loops.
- Magnetic field lines start from north pole and end at south pole of a magnet.
- The tangent at a point on a magnetic field line represents the direction of the magnetic field at that point.
- Two magnetic field lines may intersect each other.
The equivalent resistance between A and B of the network shown in figure is
A bar magnet has magnetic dipole moment . Its initial position is parallel to the direction of uniform magnetic field . In this position, the magnitudes of torque and force acting on it respectively are –
- 0 and MB
- MB and MB
- 0 and 0
Two charges 14
C and -4
C are placed at (-12 cm, 0, 0) and (12 cm, 0, 0) in an external electric field E =
where B = 1.2 x 106 N/cm2 are r is in metres. The electrostatic potential energy of the configuration is
- 97.9 J
- 102.1 J
- 2.1 J
- -97.9 J
A 300 resistor and a capacitor of F are connected in series to a 200 V - 50 Hz AC source. The current in the circuit is -
- 0.1 A
- 0.4 A
- 0.6 A
- 0.8 A
The core of a transformer is laminated to reduce the effect of:
- flux leakage
- copper loss
- hysteresis loss
- eddy current
Question No. 45 to 49 are Assertion (A) and Reason (R) type questions. Given below are the two statements labelled as Assertion (A) and Reason (R). Select the most appropriate answer from the options given below as:
- Both a. and (R) are true and (R) is correct explanation of a.
- Both a. and (R) are true and (R) is not correct explanation of a.
- (A) is true, but (R) is false.
- (A) is false and (R) is also false.
Assertion (A): A negative charge in an electric field moves along the direction of the electric field.
Reason (R): On a negative charge a force acts in the direction of the electric field
Assertion (A): The poles of a bar magnet cannot be separated
Reason (R): Magnetic monopoles do not exist
Assertion (A): When radius of a current carrying loop is doubled, its magnetic moment becomes four times.
Reason (R): The magnetic moment of a current carrying loop is directly proportional to the area of the loop
Assertion (A): Higher the range, lower is the resistance of an ammeter.
Reason (R): To increase the range of an ammeter additional shunt is added in series to it.
Assertion (A): A step-up transformer cannot be used as a step-down transformer.
Reason (R): A transformer works only in one direction.