31.

Two metal wires of identical dimensions are connected in series if σ₁a nd σ₂ are the conductivity of the metal wires respectively, the conductivity of the combination is 

• 
• 
• 
• 

A series R -C circuit is connected to an alternating voltage source. Consider tow situations:

1. When the capacitor is air filled.
2. When the capacitor is mica filled.

Current through resistor is i and voltage across capacitor is V then

• V_a < V_b

• V_a > V_b

• i_a >i_b

• i_a >i_b

A circuit contains an ammeter, a battery of 30 V and a resistance 40.8 Ω all connected in series. If the ammeter has a coil of resistance 480 Ω and a shunt 20 Ω then reading in the ammeter will be

• 0.5 A

• 0.25 A

• 2 A

• 2 A

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 potentiometer wire of length L and a resistance r are connected in series with battery of e.m.f. E_o and a resistance r₁. An unknown e.m.f is balanced at a length l of the potentiometer wire. The e.m.f E will be given by

In the spectrum of hydrogen, the ratio of the longest wavelength in the Lyman series to the longest wavelength in the Balmer series is 

• 4/9

• 9/4

• 27/5

• 27/5

A photoelectric surface is illuminated successively by monochromatic light of wavelength λ and λ/2. If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is 

(h = planck's constant, c= speed of light)

• hc/ 2λ

• hc/λ

• 2 hc/λ

• 2 hc/λ

Light of wavelength 500 nm is incident on metal with work function 2.28 eV. The de - Broglie wavelength of the emitted electrons is 

• <2.8 x 10^-10 m 

• <2.8 x 10^-9 m

• > equal  to 2.8 x 10^-9 m

• > equal  to 2.8 x 10^-9 m

The input signal given to a CE amplifier having a voltage gain of 150 is  The corresponding output signal will be

A nucleus of uranium decays at rest into nuclei of thorium and helium. Then, 

• the helium nucleus has more kinetic energy than the thorium nucleus

• the helium nucleus has less momentum than the thorium nucleus

• the helium nucleus has more momentum than the thorium nucleus

• the helium nucleus has more momentum than the thorium nucleus