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Physics
Magnetic field
Three rings, each having equal radius $R$ are placed mutually perpendicular to each other and each having its centre at the origin of the coordinate system. If current $I$ is flowing through each ring, then the magnitude of magnetic field at the common centre is:

$(A)\sqrt 3 \dfrac{{{\mu _o}I}}{{2R}}$
$(B)0$
$(C)\left( {\sqrt 2 - 1} \right)\dfrac{{{\mu _o}I}}{{2R}}$
$(D)\left( {\sqrt 3 - \sqrt 2 } \right)\dfrac{{{\mu _o}I}}{{2R}}$

Physics
Magnetic field
Magnet field at the center (at nucleus) of the hydrogen-like atoms (atomic number $= {\text{Z}}$ ) due to the motion of electron in ${{\text{n}}^{{\text{th}}}}$ orbit is proportional to
A. $\dfrac{{{{\text{n}}^3}}}{{{{\text{z}}^5}}}$
B. $\dfrac{{{{\text{n}}^4}}}{{\text{z}}}$
C. $\dfrac{{{{\text{z}}^2}}}{{{{\text{n}}^3}}}$
D. $\dfrac{{{{\text{z}}^3}}}{{{{\text{n}}^5}}}$
Physics
Magnetic field
An infinitely long cylinder is kept parallel to a uniform magnetic field $B$ directed along the positive z-axis. The direction of induced current on the surface of the cylinder as seen from the z-axis will be
A. Clockwise of the positive z-axis
B. Anticlockwise of the positive z-axis
C. Zero
D. Along the magnetic field
Physics
Magnetic field
State four properties of magnetic field lines.
Physics
Magnetic field
When a charged particle, moving with a velocity $v$ , is subjected to a magnetic field, the force on it is non-zero. This implies that:
A. Angles between them is either ${0^o}$ or ${180^o}$
B. Angles between them is necessarily ${90^o}$
C. Angles between them can have any value other than ${90^o}$
D. Angles between them can have any value other than ${0^o}$ and ${180^o}$

Physics
Magnetic field
A magnetic needle is kept in a non-uniform magnetic field. It experiences
A. A force and a torque
B. A force but not a torque
C. A torque but not a force
D. Neither a force nor a torque
Physics
Magnetic field
Two similar coils are kept mutually perpendicular such that their centers coincide. At the center, find the ratio of the magnetic field due to one coil and the resultant magnetic field through both coils, if the same current is flown.
Physics
Magnetic field
An electron is travelling horizontally towards east. A magnetic field in vertically downward direction exerts a force on the electron along
A. East
B. West
C. North
D. South

Physics
Magnetic field
What is the force on a current carrying wire that is parallel to the magnetic field? Give reason for your answer.

Physics
Magnetic field
What is our best evidence that earth has a magnetic field?
A. All things fall towards earth’s centre.
B. A compass needle lines up with it.
C. Winds blow from east to west.
D. Earth’s oceans all have currents.
Physics
Magnetic field
A charge of $+ 10$C enters a uniform magnetic field parallel to its direction. What will happen to the charge?

Physics
Magnetic field
A copper rod moves parallel to the horizontal direction. The induced emf developed across its ends due earth’s magnetic field will be maximum at the
A. Equator
B. Latitude $30$
C. Latitude $60$
D. Poles

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