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The total force on a charge q moving with velocity v in the presence of
magnetic and electric fields B and E, respectively is called the
1. lorentz force
2. daniel force
3. both
4. none of these
The magnetic force q (v × B) is normal to v and work done by it is
1. one
2. zero.
3. two
4. ten
A straight conductor of length l and carrying a steady current I experiences a force F in a uniform ...........magnetic field B,
1. external
2. internal
3. at ends
4. none of these
two charged particle traversse identical helical path in a completely opposite sense in a uniform magnetic field B=B0k^
1. they have equal z- componants of momenta
2. they must have equal charges
3. they necessarily represents a particle - antipaticle pair
4. the charge to mass ratio satisfy (e/m)1 + (e/m)2 =0
biot savart law indicates that the moving electron produce a magnetic field B such that
1. B perpendicular V
2. B parallel t V
3. it obeys inverse cube law
4. it is along the line joining the electron and point of observation
an electron is projected with uniform velocity along the axis of a current carrying long solenoid which of the following is true
1. the electron will be accelatrated along the axis
2. the electron path will be circular about the axis
3. the electron will experience a force at 45 degree to the axis a hence execute a helic path
4. the electron will continue to ove with uniform velocity along he axis of the solenoid
in a cyclotron , a changed particle
1. undergoes acceleration all the time
2. speeds up between the dees because of the magnetic field
3. speeds up in a dee
4. slow down within a dee speeds up between dees
a circular current loop of magnetic moment is in arbitary orientation in an external magnetic field B . the work done to rotate the loop by 30 degree about an axis perpendicular to its plane is
1. MB
2. 3MB/2
3. MB/2
4. zero
a circular coil of radius 4 cm and of 20 turns carries a current of 3 amperes . it is placed in a magnetic field of intensity of 0.5 weber/m2 . the magnetic dipole moment of the coil is
1. 0.15 ampere-m2
2. 0.3 ampere-m2
3. 0.45 ampere-m2
4. 0.6ampere-m2
a cubical region of space is filled with some uniform electric and magnetic field . an electron enters the cube across one of its faces with velocity v and a position enters via opposite face with velocity -v at this instant
1. the electric forces on both the particle cause identical acceleration
2. the magnetic forces on both the particle cause equal acceleration
3. only electron gain or looses energy
4. the motion of the centre of mass (cm) is determined by E alone
two identical current carrying coaxial loops , carry current I in an opposite sens a simple amperian loop passes through both of them once callling the loop as
C
1. $\oint c B . d l = \pm 2 μ o l$
2. the value of $\oint c B . d l$ is independent of sense of C.c
3. there may be a point on C where, B and dl are parallel
4. B vanishes everywhere on C
if a charged particle moves through a manetic field perpendicular to it
1. both momentum and energy are constant
2. momentum as well as energy are constant
3. energy is constant but momentum changes
4. momentum is constant but energy changes
A current carrying closed loop of an irregular shape lying in more than one placed in uniform magnetic field , the force acting on it
1. will be more in the plane where its larger position is covered
2. is zero
3. is infinite
4. may or may not be zero
the maximum current that can be measured by a galvanometer of resistance 40 ohm is 10 mA . it is converted into voltmeter that can read upto 50 V . the resistance to be connected in the series with the galvanometer is
1. 2010ohm
2. 4050 ohm
3. 5030 ohm
4. 4960 ohm
a current loop placed in a non uniform magnetic field experience
1. a force of repulsion
2. a force of attraction
3. a torque but not force
4. a force and a torque
if the beams of electron and proton move parallel to each other in the same direction then they
1. attract each other
2. repel each other
3. no relation
4. neither attract nor repel
a conducting circular loop of radius r carries a constant current i . it is placed in a uniform magnetic fied B , such that B is perpendicular to the plane of the loop . the magnetic force acting on the loop is
1. irB
2. 2 $π$ riB
3. zero
4. $π$ riB
the gyro magnetic ratio of an electron in an H - atom , according to Bohr model is
1. independent of which orbit it is in
2. neutral
3. positive
4. increases with the quantum nuber n
An electron is projected along the axis of a circular conductor carrying the same current . electron will experience
1. a force along the axis
2. a force perpendicular to the axis
3. a force at an angle of 4 degree with axis
4. no force experienced
in a circular coil of radius r , the magnetic field at the centre is propotional to
1. r2
2. r
3. 1/r
4. none of these
a positive charge enter in a magnetic field and travels parallel to but opposite the field . if experience
1. an upward force
2. a downword force
3. an accelerated force
4. no force
when a magnetic compass needle is carried nearby to a straight wire carrying current then
(i) the straight wire cause a noticeable deflection in the compass needle
(ii) the alignment of the needle is tangential to an imaginary circle with straight wire as its centre and has a plane perpendicular to a wire
1. (i) is correct
2. (ii) is correct
3. both (i) and (ii) are correct
4. neither (i) nor (ii) is correct
a strong magnetic field is applied on a stationary electron . then the electron
1. oves in the direction of the field
2. remained stationary
3. moves perpendicular to the direction of the field
4. moves opposite to the direction of the field
in an inhert frae of reference , the magnetic force on a moving charged particle is F its value in another inertial frame of refernce will be
1. remained same
2. changed due to change in the amount of charge
3. changed due to change in velocity of charged particle
4. changed due to change in field direction
which one of the following is correct statement about magnetic forces ?
1. magnetic forces always obey newton's third law
2. magnetic force do not obey newton's third law
3. for very high current , magentic forces obey newton's third law
4. inside low magnetic field , magnetic force obey newton's third law
A charged particle is moving on circula path with velocity v in a uniform field B , if the velocity of the charged particle is doubled and strength of magnetic field is halved then radius become
1. 8 times
2. 4 times
3. 2 times
4. 16 times
two a- particle have the ratio of their velocities as 3:2 on entering the field . if they move in diffrent circular path , then the ratio of the radii of their path is
1. 2:3
2. 3: 2
3. 9: 4
4. 4: 9
a charged particle is moving in a cyclotron , what effect on the radius of path of this charged particle will occur when the frequency of the ratio frequency field is doubled
1. it will also be doubled
2. it will be halved
3. it will be increased by four times
4. it will remain unchanged
the nature of parallel and dnti parallel currents are
1. parallel currents repel and anti parallel current attract
2. parallel current attract and antiparallel current repel
3. both current attract
4. both current repel
the magnetic moment of a current i carrying circular coil of radius r and number of turns N varies as
1. 1/r
2. r
3. r2
4. none of these

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