Question

A 100 W bulb together with its power supply is suspended from a sensitive balance. Find the change in the mass recorded after the bulb remains on for 1 year.

Answer 1

 $\Delta m = 3.5\times 10^{-8} kg$

Explanation:

There is a physical significance of special theory of relativity that Energy and mass are interchangeable and that is given by Einstein famous equation ,

$E = M\times C^{2}$

According to questions,

The bulb illuminates for 1 year $( 364\times 24\times 3600)$  with power of 1 W or  1 j/ s.

Total energy dissipated by the bulb in the form of light energy will be,

$100\times 365 \times 24 \times 3600 = 3.15\times 10^{9}$ j

∴ $3.15\times 10^{9} = \Delta m \times 9\times 10^{16}$

  $\Delta m = 3.5\times 10^{-8} kg$

Answer 2

Change in Mass Recorded is $3.5 \times 10^-^8$ kg

Explanation:

There is a physical significance of special theory of relativity that Energy and mass are interchangeable and that is given by Sir Einstein famous equation $E=mc^2$

So,

• Loss in the mass due to continuous illumination of bulb

According to question,

• The bulb illuminates for 1 year i.e  

$365 \times 24 \times 3600$ sec with power of 1 W or $1 Js^-^1$

Total energy dissipated by the bulb in the form of light energy will

be $100 \times 365 \times 24 \times 3600$ J  

= $3.15 \times 10^9$ J

Hence,

$3.15 \times 10^9 J = \Delta m \times 9 \times 10^1^6$

$\Delta m = 3.5 \times 10^-^8$ kg