Answer to Question #133182 in Classical Mechanics for Quanda

Question

(1) A thin metal wire , AB, is tied at the points A and B such that it is stiff. It is plucked one quarter way from one end. 

a) Name the energy changes which take place if the wire is plucked with the finger or a small piece of broom.

b) Sketch a diagram to show the appearance of the plucked wire, and indicate the distance that represents one wavelength.

(2) Explain how a bimetallic strip works in an electric iron to switch it on and off.

(3) Explain why a metal spoon, left beside a flame for a few minutes becomes so hot to touch.

Answer 1

1)

a) Potential energy changes to kinetic energy

b)

2) The thermostat in an iron generally uses a bimetallic strip. As the name implies, a bimetallic strip is made up of two different types of metal—with dissimilar coefficients of expansion—that are bonded together. This means that in the presence of heat, they expand differently. This bimetallic strip is connected to a contact spring through small pins.

At moderate temperatures, the contact point remains in physical contact with the bimetallic strip. However, when the temperature of the iron exceeds a certain limit, the strip begins to bend towards the metal with a lower coefficient of expansion. As a result, the strip ceases to be physically connected to the contact point, the circuit opens and current ceases to flow.

3)

It is because heat is transferred to your skin by conduction.