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Class 10 Class 12

A 200 W sodium street lamp emits yellow light of wavelength 0.6 um. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

• 1.5 x 1020

• 6 x 1018

• 62 x 1020

• 3 x1019

A.

1.5 x 1020

Efficient power P=

Efficient power P=

1028 Views

Is work a scalar or a vector quantity?

Work is dot product of two vectors. i.e. .

And dot product is a scalar quantity. Therefore, work is a scalar quantity.
1450 Views

What are different units of energy?

The different units of energy are :

(i) Joule
(ii) Erg
(iii) eV
(iv) KWh
(v) Calorie.

804 Views

What is watt?

SI unit of power is Watt.
773 Views

Define the unit joule.

Work done is said to be one joule if one newton of  force displaces the body through a distance of one meter in the direction of applied  force .
799 Views

Define watt.

Power is said to be one watt if one joule of work is done in one second.
860 Views