Which changes would cause an increase in the resistance of a wire? check all that apply.
increasing its temperature
decreasing its temperature
using a longer wire
using a shorter wire
using a thicker wire
using a thinner wire

The correct answers are:

increasing its temperature  

using a longer wire  

using a thinner wire

Explanation:

the resistance of a wire determines how much the wire opposes to the flow of electrical current through it.

1- When we increase the temperature of the wire, the atoms of the wire move more and faster, so if a current passes through the wire, the electrons of the current collide more with the atoms of the wire: therefore, the resistance increases.

2- When we use a longer wire, the current must flow through a longer path, therefore the electrons of the current collide more with the atoms of the wire, and the resistance increases.

3- When we use a thinner wire, we increase the cross-sectional density of atoms in the wire, therefore the electrons in the current collide more with the atoms of the wire, and the resistance increases.

Concerning 2) and 3), we can also see this effect by looking at the formula:

where R is the resistance of a wire, its resistivity, L its length and A its area. We see that when L is increased (longer wire), R increases too, and when A is decreased (thinner wire), R increases.