You have a 2.00 kg block of lead. lead melts at 327.5°c. cpb = 130.0 j/kg*c and ? hj for lead is 2.04x10^4 j/kg . say you start at room temperature (25.0°c). how much heat must you transfer to melt all the lead?

Explanation:

1) First of all, we need to calculate the heat needed to raise the temperature of the block of lead from the initial temperature (25.0 C) to the melting temperature (327.5 C). This heat is given by the equation

where

m = 2.00 kg is the mass of the block

Cpb = 130.0 J/kg*C is the specific heat capacity of lead

is the temperature difference

Substituting,

2) Now we have to calculate the amount of heat needed to completely melt the lead, which is given by:

where

Hj = 2.04x10^4 J/kg is the latent heat of fusion of lead

Substituting,

3) Therefore, the total heat needed is

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.