What do you mean by light emitteing diodes? Why are they so called? State applications of LEDs. Why we prefer LEDs over conventional incandescent lamps?

What do you mean by magnetic lines of force? Why two such lines do not cross each other?

What the help of a diagram, show that biasing of a light emitting diode (LED). Give its two advantages over conventional incandescent lamps.

Explain, with the help of a schematic diagram, the principle and working of a Light Emiting Diode. What criterion is kept in mind while choosing the semiconductor material for such a device ? Write any two advantages of light emiting diode over conventional incandescent lamps.

What do you mean by Geologial time scale? Why it is necessary to determine the age of fossils?

Why do we prefer a.c.over d.c. in the house hold power supply?

What do you mean by abnormal molecular mass ? Why do we gets abnormal molecular masses from colligative properties

What is so special about the combination e/m? Why do we not simply talk of e and m specially?

Here is a ray vec(OA) . It starts at O and passes through the point A. It also passes through the point B. Can you also name it as vec(OB) ? Why? vec(OA) and vec(OB) are same here. Can we write vec(OA) as vec(AO) ? Why or why not? Draw five rays and write appropriate names for them. , What do the arrows on each of these rays show?