IB DP Physics: SL复习笔记5.2.8 Heating Effect of Current

• When electricity passes through a component, such as a resistor, some of the electrical energy is turned into heat, therefore, increasing its temperature
  • The heat that is produced will dissipate (spread out) into the environment via thermal conduction, convection and radiation

• When electricity passes through a component, there is energy transferred to heat
• This is due to collisions between:
  • Electrons flowing in the conductor, and
  • The lattice of atoms within the metal conductor
• Electricity, in metals, is caused by a flow of electrons
  • This is called the current
• Metals are made up of a lattice of ions
• As the electrons pass through the metal lattice they collide with ions
  • The ions resist the flow of the electrons

As electrons flow through the metal, they collide with ions, making them vibrate more

• When the electrons collide, they lose some energy by giving it to the ions, which start to vibrate more
  • As a result of this, the metal heats up

• This is used to an advantage to generate heat for appliances such as electric hobs

The heating effect of current can be used for many applications such as electric hobs

• When an electrical current does work against electrical resistance:
  • Electrical energy is dissipated as thermal energy in the surroundings
  • The heat that is produced will dissipate via thermal conduction, convection and radiation

• The amount of heat produced depends on two factors:
  • Current: The greater the current, the more heat that is produced
  • Resistance: The higher the resistance, the more heat that is produced (for a given current)

• Note that reducing the resistance can cause the current to increase
  • This could actually increase the amount of heat produced

• In mechanics, power P is defined as the rate of doing work
  • The potential difference is the work done per unit charge
  • Current is the rate of flow of charge
• Therefore, the electrical power is defined as the rate of change of work done:

• The work done is the energy transferred so the power is the energy transferred per second in an electrical component

• The power dissipated (produced) by an electrical device can also be written as

• Using Ohm's Law V = IR to rearrange for either V or I and substituting into the power equation, means power can be written in terms of resistance R

• This means for a given resistor if the current or voltage doubles the power will be four times as great.
  • Which equation to use will depend on whether the value of current or voltage has been given in the question
• Rearranging the energy and power equation, the energy can be written as:

E = VIt

• Where:
  • E = energy transferred (J)
  • V = voltage (V)
  • I = current (A)
  • t = time (s)

ANSWER:   A