Two coherent sources P and Q produce interference at point A on the screen where there is a dark band that is formed between 4th bright band and 5th bright band. The wavelength of light used is 6000 Å . The path difference between  PA and QA is 

A) $1.4 \times 10^{-4}$ cm

B) $2.7 \times 10^{-4}$ cm

C) $4.5 \times 10^{-4}$ cm

D) $6.2 \times 10^{-4}$ cm


A galvanometer of resistance 30$\Omega$  is connected to a battery of emf 2 V with 1970 $\Omega$ resistance in series. A full scale deflection of 20 divisions is obtained in the galvanometer. To reduce the deflection to 10 divisions, the resistance in series required is 

A) 4030 $\Omega$

B) 4000 $\Omega$

C) 3970 $\Omega$

D) 2000 $\Omega$


The L-C  parallel resonant circuit 

A) has a very high impedence

B) has a very high current

C) acts as resistance of very low value

D) has zero impedance


In Bohr 's theory of hydrogen atom,  the electron jumps from higher orbit n to lower orbit p. The wavelength will be minimum for the transition

A) n=5 to p=4

B) n=4 to p=3

C) n=3 to p=2

D) n=2 to p=1


A disc of radius R and thickness  $\frac {R}{6}$  has moment of interia l about an axis passing through its centre and perpendicular to its plane. Disc  is melted and recast into a solid sphere. The moment  of interia of a sphere about its diameter is 

A) $\frac{l}{5}$

B) $\frac{l}{6}$

C) $\frac{l}{32}$

D) $\frac{l}{64}$