Electromagnetic Waves — Physics STD 12 Science — Question

If the threshold wavelength for sodium is 5420 Å, then the work function of sodium is

(a) 4.58 eV

(b) 2.28 eV

(c) 1.14 eV

(d) 0.23 eV

Two identical circular loops of metal wire are lying on a table without touching each other. Loop-A carries a current which increases with time. In response, the loop-B

(a) Remains stationary

(b) Is attracted by the loop-A

(c) Is repelled by the loop-A

(d) Rotates about its CM, with CM fixed

Kirchhoff ’s junction rule is a reflection of:

Silicon is a semiconductor. If a small amount of As is added to it, then its electrical conductivity

(a) Decreases

(b) Increases

(c) Remains unchanged

(d) Becomes zero

In summer, a mild wind is often found on the shore of a calm river. This is caused due to,

1. Difference in thermal conductivity of water and soil.
2. Convection currents.
3. Conduction between air and the soil.
4. Radiation from the soil.

Which of the following statements is not correct?

A condenser of capacitance 10 μF has been charged to 100 volts. It is now connected to another uncharged condenser in parallel. The common potential becomes 40 volts. The capacitance of another condenser is

(a) 15 μF

(b) 5 μF

(c) 10 μF

(d) 16.6 μF

The capacitance of an air filled parallel plate capacitor is 10μμF . The separation between the plates is doubled and the space between the plates is then filled with wax giving the capacitance a new value of 40. The dielectric constant of wax is

(a) 12.0

(b) 10.0

(c) 8.0

(d) 4.2

Calculate the current through a lamp of 25w operating at 220v.