Physics Topic 2

• How is energy supplied to cells?

  Via electrons by a cell/battery or mains electricity, which then move through the wires to transfer energy
• What form of potential energy are cells/batteries?

  Chemical
• What does current/charge always flow from?

  From + to -
• What are electrons grouped into?

  Coulombs of charge (c)
• What is potential difference and how is it calculated?

  Measure of how much energy is transferred to/by each coulomb of electrons/charge. Unit: Volt (v)

  V = E/Q

  V = p.d. (v)

  E = energy transferred (j)

  Q = charge (c)
• What is current and how is it calculated?

  The rate of the flow of charge (how many coulombs pass every second). Unit: Amps/Amperes (A)

  I = Q/t

  I = Current (A)

  Q = Charge (c)

  t = time (s)
• What are voltmeters?

  An instrument used to measure volts. They're always connected in parallel to components.
• What are ammeters?

  Instrument used to measure amperes/amps. They're always connected in series with components.
• What is resistance?

  The measure of how much a component/object resists the flow of current. Unit: Ohms (Ω)
• How do we calculate Ohm's Law?

  V = I x R

  V = p.d. (v)

  I = current (A)

  R = resistance (Ω)
• What happens to the resistance in a resistor, filament lamp & diode?

  Resistor - Resistance remains constant as current changes.

  Filament lamp - Resistance increases as temperature of filament lamp increases.

  Diode - Has very high resistance in the reverse direction.
• What happens in series circuits?

  • Total p.d. is shared between all components
  • Current is the same for all components
  • Total resistance = sum of resistances
• What happens in parallel circuits?

  • p.d. for each branch = p.d. of cell/battery
  • current is split between the branches
  • adding more resistors in parallel reduces the total R
• What are thermistors?

  Opposite to a metal filament: if temperature increases, resistance decreases
• What are LDRs?

  Light dependent resistors are similar to a thermistor, but for light: if light intensity increases, resistance decreases?
• What can LDRs and Thermistors both be used in?

  Potential divider circuits to detect changes in environment.
• How else can power be calculated?

  P = VI or P = I^2 R
• What is alternating and direct current?

  Alternating - results from an alternating p.d.

  Direct - results in d.c.
• What are the three wires found in plugs?

  Neutral (blue) stays at 0V

  Live (brown) changes positive & negative potentials, which average out to a p.d. of 230V

  Earth (yellow & green) a safety feature that acts as an escape route for currents that could cause a shock
• What is the UK mains voltage?

  230V
• What is the national grid?

  Power stations produce a high current, that if went straight into the grid, a huge amount of energy/power would be loss as heat due to resistance of cables

  Step-up transformers increase voltage, which decreases current, reducing the power lost due to heating in cables.

  Step-down transformers reduces voltage down to 230V
• What is static electricity?

  When electrons are transferred between insulating materials
• How does static electricity work in objects?

  Electrons are negatively charged, so if an object gains electrons, it becomes negatively charged. If it loses them, it becomes positively charged
• What happens with opposite & similar charges?

  Opposites - attract

  Similar - repel
• What produces an electric field?

  Any charged object