Question

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 r and 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

please do all of them 6 ,7 ,and 8

Answer 1

(6) option B

Ampere's law can be stated as "The magnetic field created by an electric current is proportional to the size of that electric current with a constant of proportionality equal to the permeability of free space.”

So Ampere's law is used to calculate magnetic field due to distribution of electric current.

(7) option D

Radius of the circular path covered by particles of mass m and charge q in a magnetic field B in mass spectrometer is given by: r=mv/qB. So radius of circular path is directly proportional to mass of particle.

Therefore for two charged particles of same charge value, the radius of circular motion is less for lower mass and more for higher mass.

(8) Option D

Intensity is given by power per unit area. For circular cross section, intensity is power divided by area which is (pi*r^2). So intensity, I=P/(pi*r^2).

Now if radius is changed from r to r/2 keeping power same as P. Intensity changes from I to 4I because I'=P/(pi*(r/2)^2) = 4P/(pi*r^2) = 4I. Therefore intensity of laser beam becomes four times.