31.

A current loop in a magnetic field

• experiences a torque whether the field is uniform or non-uniform in all orientations

• can be in equilibrium in one orientations

• can be an equilibrium in two orientations, both the equilibrium states are unstable

• can be an equilibrium in two orientations, both the equilibrium states are unstable

A bar magnet of length l and magnetic dipole moment M is bent in the form of an arc as shown in figure, The new magnetic dipole moment will be

• M

• 3M/π

• 2M/π

• 2M/π

The output (X) of the logic circuit shown in a figure will be.

• 
• 

• X = A. B

• X = A. B

In a common emitter (CE) amplifier having a voltage gainG, the transistor used has transconductance 0.03 mho and current gain 25. If the above transistor is replaced with another one with transconductance 0.02 mho and current gain 20, the voltage gain will

• 2/3 G

• 1.5 G

• 1/3 G

• 1/3 G

In an n-type semiconductor, which of the following statement is true?

• Electrons are majority carriers and trivalent atoms are dopants

• Electrons are minority carriers and pentavalent atoms are dopants

• Holes are minority carriers and pentavalent atoms are dopants

• Holes are minority carriers and pentavalent atoms are dopants

A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, then which of the following statements is correct ?

• Diffraction pattern is not observed on the screen in the case of electrons.

• The angular width of the central maximum of the diffraction pattern will increase

• The angular width of the central maximum will decrease

• The angular width of the central maximum will decrease

In young's double-slit experiment, the slits are 2 mm apart and are illuminated by photons of two wavelengths λ₁ = 12000 A and λ₂ =10000 A. At what minimum distance from the common central bright fringe on the screen 2 m from the slit will a bright fringe from one interference pattern coincide with a bright fringes from the other?

• 8 mm

• 6 mm

• 4 mm

• 4 mm

For a normal eye, the cornea of eye provides a converging power of 40 D and the least converging power of the eye lens behind the cornea is 20 D. Using this information, the distance between the retina and the cornea eye lens can be estimated to be

• 5 cm

• 2.5 cm

• 1.67 cm

• 1.67 cm

A plano-convex lens fits exactly into a Plano-convex lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices  and  and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is

The wavelength λ_e of an electron and λ_p of a photon of same energy E are related by