A straight conductor of uniform cross-section carries a current I. Let S be the specific charge of an electron. The momentum of all the free electron per unit length of the conductor due to their drift velocity only, is

1.  I.S

2.  

3.  

4.  

 

A ray of light travelling in water is incident on its surface open to air. The angle of incidence is θ, which is less than the critical angle. Then there will be,

 

1. only a reflected ray and no refracted ray

What is the refraction index of the material of a plano-convex lens, if the radius of curvature of the convex surface is \(10\) cm and focal length of the lens is \(30\) cm?

1. \(1/3\)

A parallel plate capacitor of capacitance C is connected to a battery and is charged to a potential difference V. 
Another capacitor of capacitance 2C is connected to another battery and is charged to potential difference 2V. The charging batteries are now disconnected and the capacitors are connected in parallel to each other in such a way that the positive terminal of one is connected to the negative terminal of one is connected to the negative terminal of the other. The final energy of the configuration is

1.  Zero

The n rows each containing m cells in series are joined in parallel. Maximum current is taken from this combination across an external resistance of 3 Ω. If the total number of cells used is 24 and internal resistance of each cell is 0.5 Ω, then

 

1.  m = 8, n = 3

If the intensities of the two interfering beams in Young’s double-slit experiment are  and  then the contrast between the maximum and minimum intensities are good when

1.  is large

A simple telescope, consisting of an objective of focal length 60 cm and a single eye lens of focal length 5 cm is focused on a distant object in such a way that parallel rays emerge from the eye lens. If the object makes an angle of 2 º at the objective, then the angular width of the image is

 

1. 10 º

A semiconductor has an electron concentration of per  and a hole concentration of  per . The electron mobility is 25000   and the hole mobility is 100  . Then,

1.  the semiconductor is n-type

2.  the conductivity is 320 m mho 

3.  Both (a) and (b)

4.  None of the above

An ammeter and a voltmeter are joined in series to a cell. Their readings are A and V respectively. A resistance is now joined in parallel with the voltmeter. Then,

 

1.  Both A and V will increase