Question

4) A wire is carrying a current of I and it is placed in a magnetic field of B, the force on the wire is zero if: A) The length of wire is infinite. B) If there is a non-zero angle between magnetic field B and current I. C) The direction of the current and magnetic field are perpendicular. D) The current and magnetic field are parallel. E) There is a 90 degree angle between current direction and magnetic field direction 5) The force between two parallel wires carrying electric current is repulsive when: A) The magnitude of the current of both wires are the same. B) The direction of current in wires are opposite. C) One of the wires is carrying no current. D) The direction of the currents in wires are the same. E) Wires carrying different current values. 6) Ampere's law provides a convenient way of calculating: A) Electric field due to current distribution. B) Magnetic field due to distribution of electric current C) The force between a numbers of wires carrying current. D) Magnetic force on a wire carrying current E) Magnetic field due to charge distribution 7) Which one of the following is not correct about mass spectrometer? A) Particles regardless of mass and charge enter to the second magnetic field with same velocity. B) Charges with same charge value can enter into the second magnetic field. C) For two charges with same charge value, the radius of the circular motion is smaller for particle with less mass. D) For two charges with same charge value, the radius of the circular motion is larger for particle with less mass. E) Mass spectrometer is capable of measuring a number of masses at the same time. 8) A laser beam has a circular cross section with radius of rand power P. If we focus this laser beam with the same power P to a smaller radius of r/2, the intensity of the laser beam becomes: A) half B) twice C) one-quarter D) four times E) eight times

Answer 1

4) The force on the wire is zero if, the current and magnetic field are parallel. (Ans : D)

5) The force is repulsive when the direction of current in wires are opposite. (Ans : B)

6) Ampere's law provides a convenient way of calculating magnetic field due to distribution of electric current. (Ans : B)

7) The incorrect statement is "For two charges with same charge value, the radius of circular motion is larger for particle with less mass" (Ans : D) (radius is directly proportional to mass)

8) The intensity of laser beam becomes 4 times. (Ans: D) ( intensity is inversely proportional to r² )