Physics Ch. 1.5 and 2.3 Flashcards
What is a bi metallic strip
When strips of two different metals which expand differently upon heat are combined together they form a bi metallic strip. Brass and iron are combined to create a bi metallic strip. Brass expands more than iron.
What are three uses of a bi metallic strip
thermostat, fire alarms car indicator
What allows us to make a bi metallic strip
Different metals expand differently upon heat. The difference in expansion between different metals allows us to make a very useful device known as a bi metallic strip. Brass and iron are combined to create a bi metallic strip. Brass expands more than iron.
What happens when a strip is heated
When a strip is heated, since brass expands more than iron, it forms the outside of the curve and the strip is bent downwards.
What are the three ways of heat transfer
Conduction, convection, radiation
what is conduction
Conduction takes place in solids, especially metals. Conduction is the transfer of heat through a material from points of high temperature to points of low temperature.
The whole process of conduction
When one end of a metal bar or iron rod is heated, the molecules at that end begin to vibrate rapidly because it gains energy. This makes the nearby molecules at the cooler end vibrate more as they are bumped by the hot molecules. Eventually the molecules vibrate faster all along the bar. Heat energy is thus being transferred from the hot end to the cold end.
Examples of conductor
gold, silver, aluminium
Examples of insulators
plastic, glass, wood
Why are bottoms of saucepans made of aluminium and handles made of plastic
Aluminium is a good conductor of heat. This means that it allows heat energy to pass through it. On the other hand, plastic is an insulator, meaning it does not allow heat to pass through. Thus, the plastic is used in the handle to stop heat from travelling from the hot saucepan to our hand and burning it.
What is convection
It takes place in liquids and gases (fluids). Convection is the transfer of heat through a fluid by the actual movement of the fluid itself.
____,____ ______ rises to the top and ____, ____ ____ sinks to the bottom
Hotter, less dense air
Colder, more dense air
What is radiation
(Unlike conduction and convection) radiation requires no material medium (metal, liquid or gas). It can travel thoroughly through an empty space or vacuum.
Why do people wear dark clothes in the winter and light clothes in the summer
People often wear dark clothes in winter and light clothes in summer, This is because the heat from the sun travels directly to the dark and light surface reflects the heat rays from the sun while the dull, dark surface takes them in. White and shiny surfaces are good reflectors of heat and light rays. Black surfaces are good absorbers. In summer a white shirt reflects the sun’s rays and you stay cooler. A black shirt absorbs the sun’s rays and warms you up.
Many insulators contain tiny pockets of ______
trapped air (e.g. wool vests/sweaters and blankets)
