Question

Electromagnetic radiation of wavelength 300 Ao is made to fall on a metal with work function 35.15eV. If 1020 photons are hitting the metal surface per second, find the power consumed by a battery connected in reverse bias, to maintain the photo current produced at zero amperes. Express answer in Joules/sec
PLEASE ITS IMPORTANT

Answer 1

(a) concentration of solution is 5 M, it means 5 mol of urea is present in 1000 ml of solution.

mass of solution = volume of solution × density of solution

= 1000 ml × 1.5 g/ml = 1500 g

mass of solute = no of moles of solute (urea) × molar mass of solute

= 5 mol × 60 g/mol = 300 g [ ∵ molar mass of urea is 60 g/mol ]

now mass of solvent = mass of solution - mass of solute = 1500 g - 300 g = 1200 g

now molality = no of moles of solute/mass of solvent in kg

= 5/(1200/1000) = 5/1.2 = 4.167 molal

Therefore the molality of the solution is 4.67 molal