Physics U4 - Energy Resources and Transfers

How can energy be transferred?

• Mechanically

• Electrically

• By heating

• By radiation

What is the principle of conservation of energy?

• Energy cannot be created or destroyed, it can only be transferred from one form to another

• Energy input = energy output

Efficiency formula

(Useful energy output / total energy input) x 100%

Define conduction

• Thermal energy being transferred by the vibration of particles in solids and liquids

What are insulators

• Materials that transfer heat slowelu

  • Usually non-metals

• To reduce heat transfer .e.g. to keep homes warm

Describe a metal conducting heat

• As metals are heated, delocalised electrons that a vibrate more and collide throughout the metal to transfer heat from hotter parts to cooler parts

What is convection?

• Thermal energy transfer in fluids

Describe what happens when a fluid is heated through convection

• Particles vibrate faster and move further apart (they expand)

• This makes them less dense

• Hot fluid rises to less dense areas

• Cooler fluid sinks down to take the place of the more dense areas

What type of radiation transfers thermal energy?

• Infrared radiation (part of the EM spec)

  • Does not need a medium

How do black and white colours affect radiation?

• Black bodies are absorbers and emitters of radiation

• White bodies are reflectors of radiation

How does temperature and surface area of a body affect the rate of absorption or reflection of radiation?

• The higher the temperature, the more radiation is emitted

  • Hotter objects contain more energy so they give out more energy as radiation

• The greater the surface area, the more radiation is emitted or absorbed

  • This is because there is more area where radiation can be emitted or absorbed from

What is work done?

Energy changing forms

State the equation for work done

Work done = force x distance

What is the equation linking kinetic energy, mass and speed?

Kinetic energy = 0.5 x mass x speed²

What is the equation linking gravitational potential energy, mass, gravitaitonal field strength and height?

Gravitational potential energy = mass x gravitational field strength x height

What is power?

The rate at which energy is transferred (the rate at which work is done)

What is the equation linking power, work done and time?

Power = work done (energy transferred) / time

Describe a practical to investigate the rate of conduction of different materials

• Set the apparatus as follows

• Attach ball bearings to the end of each metal strip using wax

  • make sure each strip equal in length from the ring.

• The strips should be heated gently with a bunsen burner

• The wax will melt and the ball bearings will drop

• Time how long it takes for each ball bearing to drop

• Repeat the experiment and calculate an average of each time

Describe a practical to investigate the affect of different temperatures on the rate of convection

• Set the apparatus as follows

• Fill the beaker with cold water and place it on top of a tripod

• Place Potassium Manganate (VII) crystals at the bottom of the beaker using forceps

• Heat the beaker using a bunsen burner and record observations

Describe a practical to investigate the affect of colour on the radiation

• Set up four identical flasks with different shades of black and white

• Fill flasks with hot water

• Note the starting temperature and measure the temperature at regular intervals