Electrical Question 3

Slide 1

Slide 2

• Calculate the resistance of a 20Cm circular piece of copper wire with a radius of 12mm. give your answer to two significant figures
• p= 17.2
• l= 20 cm
• A= piR2 = pi x 12 squared
• A=452 - have to convert from
• MM to CM so divide by 10
• R= 17.2 x20/45.2
• R= 7.6

Slide 3

Slide 4

• a) Calculate the resistance of the rotor winding given
• that aluminium has a resistivity of 28.6μΏmm. Express your answer in milliohms
• to 3 significant figures
• p= 28.6
• L= 96m
• A= base x height
• A = 1.5 x 2.1
• A =3.15
• R= ?
• 28.6 x 96 = 872Miliohms
• 3.15
• R= 872 Miliohms

Slide 5

Slide 6

• A) Calculating Resistance of the wire
• Step one: put the figures in the
• above formula
• R=?
• P= 17.2 x 10-9 Ώm
• L=
• 12
• A= 0.6 x 10-6
• R=
• pL R = 17.2
• x10-9 x12 R = 344 Ώm R = 344 x 10-3 = 0.344 Ώ
• A 0.6x
• 10-6
• R=0.344 Ώ
• B) Calculate
• the resistance of a cable made from 30 strands of this wire
• We know the resistance from one
• cable is 344 miliohms so we divide this by 30 (the number of wires) to find
• total resistance
• 344 Miliohms = 11.47 Ώm
• to three significant figures it
• is 11.4Ώm
• 30