Question 15
The diagram shows four rods. Each rod is made of a different metal.

Wax is used to attach small metal balls at the rod ends P, Q, R and S.
Each rod is the same size. They are heated uniformly by a Bunsen burner at point X.
As the rods warm up, the wax melts and the balls fall off.
Why does the ball on the silver rod fall first?

Wax is used to attach small metal balls at the rod ends P, Q, R and S.
Each rod is the same size. They are heated uniformly by a Bunsen burner at point X.
As the rods warm up, the wax melts and the balls fall off.
Why does the ball on the silver rod fall first?
