CH.27

A cylindrical wire has resistance R and resistivity p. If its length and diameter are BOTH cut in half, what will be its resistance?

• 2R

• (1/2)R

• 4R

• (1/4)R

When a potential difference of 10V is placed across a solid cylindrical resistor, the current is 2A. If the diameter is tripled, what will the current be?

• (9/5) A

• (5/9) A

• 3 A

• (1/3) A

If a current of 2.4A is flowing in. a cylindrical wire of diameter 2.0mm, what is the average current density in this wire?

You are given a copper bar of dimensions 3cm x 5cm x 8cm and asked to attach leads to it in order to make a resistor. If you want to achieve the LARGEST possible resistance, you should attach leads to the opposite faces that measure:

• 5cm x 8 cm

• 3cm x 5cm

• 3cm x 8cm

• Any pair of faces produces the same resistance

A 5 ohm resistor and a 9 ohm resistor are connected in parallel. A 4.0 ohm resistor is then connected in series with this parallel combination. An ideal 6.0V battery is then connected with the series-parallel connection. What is the current through the 4 ohm resistor?

• 1.2 A

• 0.83A

• 2 A

• 7.21 A