Electrical Power | Physics for GCSE/IGCSE - Year 11 PDF Download

Electrical Power Equation

•  In mechanics, power (P) represents how quickly work is performed.
  • Potential difference denotes the amount of work conducted per unit charge.
  • Current signifies how quickly charge moves through a circuit.
• Therefore, electrical power is described as the rate at which work done alters.

• The work done corresponds to the energy transferred, hence power denotes the energy transferred per second within an electrical component.
• The power either dissipated or produced by an electrical device can also be expressed as:
  
• Utilizing Ohm's Law V = IR and rearranging for either V or I, then substituting into the power equation, allows power to be expressed in terms of resistance R.
  
• For a given resistor, if the current or voltage doubles, the power will increase fourfold. 
  • The choice of equation to use depends on whether the question provides the value of current or voltage.
• Rearranging the energy and power equation, the energy can be expressed as:
  E = VIt
• Where:
  • E = energy transferred (J)
  • V = potential difference (V)
  • I = current (A)
  • t = time (s)

Measuring Energy Usage

• Energy consumption in households and businesses is typically measured and compared using a unit known as the kilowatt hour (kWh).
• The kilowatt hour is essentially defined as the amount of energy equivalent to one kilowatt of power being consumed for one hour.
• Appliances are assigned power ratings, which provide information to consumers regarding the rate of energy transfer to the device per second.

• Energy usage is commonly quantified in kilowatt-hours (kWh), which is then utilized to determine the overall cost of energy consumed.

Calculating with kWh

• The kilowatt-hour (kWh) can also be mathematically expressed through an equation.
  E = Pt
• The energy equation involves key variables:
  • E = energy (kWh)
  • P = power (kW)
  • t = time (h)
• This equation stands out because it doesn't use the standard International System of Units (S.I.). Both energy and power are multiplied by 10³, and time is measured in hours instead of seconds.
• Considering the typical unit for energy is joules (J), where 1 Watt (W) equals 1 joule per second, i.e., 1 W in 1 s.
• Therefore,
  
• Given 1 kW = 1000 W and 1 h = 3600 s
• Conversion from Joule to kW h:
  
• The kilowatt-hour (kWh) is a significant unit of energy, commonly employed to measure energy consumption in various settings such as homes, businesses, factories, and other industrial applications.