Question

2.2) In electrical conduction, what is the difference between resistance and resistivity? (4 marks] 2.3) Calculate the total resistance of a 100 metre roll of 2.5 mm copper wire if the resistivity of copper at 20°C is 1.72 x 10 m. (5 marks) 2.4) X-rays of 0.1542 nm (K alpha line) are diffracted from a crystal of table salt, NaCl. The first order Bragg diffraction peak was found at an angle of 15.9º. Calculate the spacing between the diffracting planes in NaCl. Show your working (5 marks)

Answer 1

1)

resistance (R) => opposes the flow of free electrons

SI unit =Ω

it depend on Length, cross-section area of conductor and temperature.

resistivity (ρ) = > the property of the material which defines the resistance of the material having specific dimension.

it depends on  temperature only

SI UNIT = Ω.m

relations between them

R = ρ L/A

L = length and A is area of cross section of wire

2)

ρ = 1.72*10^-8*

L = length of wire = 100 m

A = area of cross section = 2.5mm² = 3*10^-6 m²

R = ρ L/A = 1.72*10^-8* 100/ ( pi*2.5*10^-6) =

  R = 0.218997202 Ω

3)

n = 2d sin

first order n = 1

d =  n / 2*sin

= 1 *0.1542 nm / ( 2*sin15.9)

d =0.2814 nm (nanometers) answer

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