Question

jb

4a) A light beam with a wavelength of 4.1 x 10^-7m and intensity of 212 W/m^2 shines on a target of an area of 3.5m^2. How many photons per second are striking the target?

b). A particle of matter is moving with a kinetic energy of 6.2eV. It's de Broglie wavelength is 6.7 x 10^-10m. What is the mass of the particle?

c) Two spaceships are traveling with the relative velocity of 1.7 x 10^8 m/s. Both carry identical clocks. According to the captain of each ship, the other captain's clock ticks more slowly than his own. By what factor do the two clocks disagree?

Answer 1

[a] ans

now we find the power

power P=212*3.5=742 W

now we find the energy

energy E=6.62*10^-34*3*10^8/4.1*10^-7

=4.84*10^-19 J

the number of photons per second =P/E=742/4.84*10^-19=153.31*10^19

[b] ans

step;1

Given that

wavelength=6.7*10^-10 m

k.E=6.2*1.6*10^-19=9.92*10^-19 J

step;2

now we find the momentum

momentum =h/wavelength=6.63*10^-34/6.7*10^-10=0.9896*10^-24 kg.m/s

now we find the mass

mass =p^2/2E=(0.9896*10^-24)^2/2*9.92*10^-19

=0.97931*10^-48/19.84*10^-19

=0.494*10^-30 kg