NEET Physics : Moving Charges And Magnetism

An electron moves on a straight line path XY as shown. The abcd is a coil adjacent in the path of the electron. What will be the direction of the current, if any induced in the coil?

• abcd

• adcb

• the current will reverse its direction as the electron goes past the coil

• the current will reverse its direction as the electron goes past the coil

A galvanometer of resistance, G is shunted by a resistance S ohm. To keep the main current in the circuit unchanged,the resistance to be put in series with the galvanometer is

A thermocouple force towards the conductor produces an emf of 40 μ V/^oC in the linear range of temperature. A galvanometer of resistance 10 Ω whose sensitivity is 1μA/div, is employed with the thermocouple. The smallest value of temperature difference that can be detected by the system will be.

• 0.5^oC

• 1^oC

• 0.1^oC

• 0.1^oC

Charge q is uniformly spread on a thin ring of radius R. The ring rotates about its axis with a uniform frequency f Hz. The magnitude of magnetic induction at the centre of the ring is 

• μ_oqf  / 2R

• μ_oq / 2fR

• μ_oq / 2πfR

• μ_oq / 2πfR

A short bar magnet of magnetic moment 0.4 JT^-1 is placed in a uniform magnetic field of 0.16T. The magnet is stable equilibrium when the potential energy is

• -0.64 J

• zero

• -0.082 J

• -0.082 J

A potentiometer circuit is set up as shown. The potential gradient across the potentiometer wire is k volt /cm and the ammeter, present in the circuit, reads 1.0 A when the two-way key is switched off. The balance points, when the key between the terminals (i) 1 and 2 (ii) 1 and 3, is plugged in, are found to be at lengths  l₁ and l₂ cm respectively. The magnitudes, of the resistor R and X, in ohm, are then, equal respectively, to

 

• k (l₂ -l₁) and kl₂

• kl₁ and k (l₂-l₁)

• k (l₂ - l₁) and kl₁

• k (l₂ - l₁) and kl₁

A galvanometer has a coil of resistance 100 Ω and gives a full-scale deflection for 30 mA current. If it is to work as a voltmeter of 30 V range, the resistance required to be added will be

• 900 Ω

• 1800

• 500 Ω

• 500 Ω

A square current carrying loop is suspended in a uniform magnetic field acting in the plane of the loop. If the force on one arm of the loop is , the net force on the remaining three arms of the loops is

• 3 

• -

• 
• 

A particle having a mass of 10^-2 kg carries a charge of 5 x 10^-8 C. The particle is given an initial horizontal velocity of 10⁵ ms^-1 in the presence of electric field and magnetic field. To keep the particle moving in a horizontal direction. it is necessary that

1)  should be perpendicular to the direction of velocity and  should be along the direction of velocity

2) Both  and  should be along the direction of velocity.

3) Both  and  are mutually perpendicular and perpendicular  to the direction of  velocity

4)  should be along the direction of velocity and  should be perpendicular to the direction of velocity.

• (1) and (3)

• (3) and (4)

• (2) and (3)

• (2) and (3)

A current loop consists of two identical semicircular parts each of radius R, one lying in the x-y plane and the other in x-z plane.  if the current in the loop is i. The resultant magnetic field due to the two semicircular parts at their common centre is