Specific heat of water is 4.2 J/gå¡C. If light of frequency 3 ÌÑ 109 Hz is used to heat 400 gm of water from 20å¡C to 40å¡C, the number of photons needed will be
2.80 × 104
1.69 × 1029
2.80 × 105
1.69 × 1028
