Question

Help with 7 , 8 , and 9 anyone?

Answer 1

Seven

Formula

I'm assuming that the formula used is

R = R_ref [1 + α*(T - T_ref)=

Givens

• R_ref is the starting resistance of 100 ohms
• α (alpha) = 4.0 *10^-4 or 0.00040
• T_ref = 11.5 degrees Celcius
• T = 10 degrees.
• R=??

Solution

R = 100[ 1 + 4.0*10^4(10 - 11.5)]           Collapse the brackets.

R = 100[ 1 + 4.0*10^4(-1.5)]                  Simplify

R = 100[1 -  0.00060]                          Subtract

R = 100[0.9994]                                  Multiply

R = 99.94

Answer: A

Eight

The accepted formula for resistance and resistivity is

R = ρ * A / L where

rho is the resistivity

A is the face Area of the conductor

L is the length of the conductor.

Now a perfect conductor has a resistance of 0.

So since resistivity is a direct variation with resistance, its value also has to be 0.

Answer: A

Nine

The formula you need for this is W = I^2* R

W = 14 Watts

R = 17 ohms

I = ??

14 = I^2 * 17       Divide bother sides by 17

14/17 = I^2

0.8235 = I^2      Switch and take the square root of both sides.

I = sqrt(0.8234)

I = 0.9075           Answer: D