Unit 3

• define current?

  a flow of electrons due to a potential difference
• Define DC current?

  electrons flow in only one direction
• define AC current?

  current changes direction and size with time
• AC or DC?

  AC

  
• AC or DC?

  DC

  
• Stated mains voltage in UK?

  230V
• mains frequency in uk?

  50 Hz
• peak voltage of mains in uk?

  325V
• How to find Vpeak off of a diagram?

  multiply y-gain by number of divisions from axis to crest
• Vpeak is always larger than Vrms
• what is Vrms?

  stated voltage
• voltage increases as current increases, as long as the resistance remains constant
• what extra equation joins Ipeak and Vpeak?

  Vpeak = Ipeak x R , where R is resistance
• what extra equation joins Irms and Vrms?

  Vrms = Irms x R , where R is resistance
• how to find frequency of a wave from an oscilloscope ?

  f = 1/T
• Define resistance ?

  the ability of a material to oppose the flow of charge (current)
• Units for resistance?

  Ohm (Ω)
• how to calculate total resistance in series?

  Rt = R1 + R2 + R3
• How to calculate total resistance in parallel?

  1/Rt = 1/R1 + 1/R2 + 1/R3
• apparatus for measuring resistance ?

  ohmeter
• Define power?

  the energy transferred per second
• define EMF?

  the energy per charge that’s gained from the source
• what does an EMF of 12V mean?

  12 joules per coulomb of charge is gained from the battery
• how can the internal resistance be estimated?

  short circuit
• The EMF is measured as the voltage across the source when there is no load resistance
• What is TPD?

  the voltage measured across the terminals when current is flowing
• The difference between the EMF and TPD is called the lost volts
• E = V + Ir, what is E?

  EMF
• E = V + Ir, what is V?

  TPD
• E = V + Ir, what is Ir?

  lost volts
• how to calculate internal resistance (r) from a TPD/current graph?

  -m , m being the gradient
• how to calculate EMF from a TPD/current graph?

  y intercept
• how to calculate short circuit current from a TPD/current graph?

  extend to x axis
• what is a capacitor made from?

  2 metal plates separated by an insulator
• A capacitor stores charge and energy
• when is a capacitor fully charged?

  when the voltage across it is equal to the supply voltage
• Define capacitance?

  the charge per unit volt
• Units for capacitance?

  Farads (F)
• 1 farad is equal to 1 coulomb per volt
• Charge is directly proportional to voltage