P.3.5.1.3 Resistivity

A student carries out an experiment to determine the resistivity of a metal wire. She determines the resistance from measurements of potential difference between the ends of the wire and the corresponding current. She measures the length of the wire with a ruler and the diameter of the wire using a micrometer. Each measurement is made with an uncertainty of 1%

Which measurement gives the largest uncertainty in the calculated value of the resistivity?

• current

• diameter

• length

• potential difference

The two resistors shown are both uniform cylinders of equal length made from the same conducting putty.

The diameter of Y is twice that of X. The resistance of Y is R.

What is the total resistance of the combination?

• $\frac{4R}{5}$

• 3R

• 4R

• 5R

Which statement about superconductors is correct?

• When a material becomes a superconductor, its resistivity is almost zero.

• The temperature at which a material becomes a superconductor is called the critical temperature.

• When current passes through a superconductor the pd across it becomes a maximum.

• Copper is a superconductor at room temperature.

A wire has a resistance R.

What is the resistance when both the length and radius of the wire are doubled?

• $\frac{R}{4}$

• $\frac{R}{2}$

• 2R

• 4R

Which graph shows the variation of the resistance with temperature for an ntc thermistor?

• A

• B

• C

• D

The table shows the resistivity, length and cross-sectional area of wires P and Q.

The resistance of wire P is R.

What is the total resistance of the wires when they are connected in parallel?

• $\frac{R}{9}$

• $\frac{R}{3}$

• $\frac{2R}{3}$

• $\frac{3R}{2}$

When the temperature of a copper wire increases, its ability to conduct electricity

• remains the same.

• increases

• decreases

• remains the same at first and then increases

A metal wire has a length l and a cross-sectional area A. When a potential difference V is applied to the wire, there is a current I in the wire.

What is the resistivity of the wire?

• 
• 
• 
• 

When a constant potential difference (pd) is applied across the ends of a uniform wire there is a current I in the wire.

The wire is replaced by one made from the same material, but of double the length and double the diameter. The same pd is applied across the ends.

What is the new current?

• 4I

• 2I

• $\frac{I}{2}$

• $\frac{I}{4}$

A cylindrical conductor of length l, diameter D, and resistivity ρ has a resistance R.

What is the resistance of another cylindrical conductor of length l, diameter D/2, and resistivity ρ?

• 8R

• 4R

• 2R

• R