Alternating Current and Voltage

• What is defined as alternating current (a.c)?

  A current that varies between positive and negative
• How does the direction of alternating current change?

  It varies every half cycle
• What shape describes the variation of current or p.d. with time in a.c?

  A sine curve
• How do electrons behave in a wire carrying a.c?

  They move back and forth with SHM
• What is the relationship between time period T and frequency f for a.c?

  f = 1/T
• What is peak current (I)?

  The maximum value of alternating current
• How can peak current or voltage be determined?

  From the amplitude of a current-time graph

  
• What is peak-to-peak current or voltage?

  The distance between positive and negative peaks
• How is peak voltage (V) calculated?

  V = peak-to-peak voltage ÷ 2

  
• What are root-mean-square (rms) values used for?

  Comparing a.c to equivalent d.c values

  
• What do rms values represent?

  Values producing the same heating effect as d.c
• How is the rms value of an alternating current defined?

  Square root of the mean of the squares

  
• What is the equation for rms current (I_rms)?

  I_rms = 0.707 × I
• How is rms voltage (V_rms) defined?

  Square root of the mean of the squares of voltage

  
• What is the equation for rms voltage (V_rms)?

  V_rms = 0.707 × V

  
• What does the rms value deliver in a resistor?

  Same average power as a.c
• What is a resistive load?

  An electrical component with resistance
• What is the average power of a supply?

  Product of rms current and voltage

  
• What is the mains electricity supplied in the UK?

  230 V at 50 Hz
• How does mains voltage vary?

  It varies depending on demand and supply
• Which devices use a.c from the mains?

  Lamps, heaters, and large electric motors
• How do most devices like computers operate?

  They use d.c converted from a.c
• What is the equation for peak voltage (V_p)?

  V_p = √2 × V_rms

  
• How is peak-to-peak voltage calculated?

  Peak-to-peak voltage = V_p × 2

  
• What is the peak-to-peak voltage for a 230 V rms supply?

  651 V (3 s.f)
• What should you double-check on alternating current graphs?

  The units on the x-axis
• Why is it important to check the x-axis units?

  They are often shown in milliseconds
• What is defined as alternating current (a.c)?

  A current that varies between positive and negative
• How does the direction of alternating current change?

  It varies every half cycle
• What shape describes the variation of current or p.d. with time in a.c?

  A sine curve
• How do electrons behave in a wire carrying a.c?

  They move back and forth with SHM
• What is the relationship between time period T and frequency f for a.c?

  f = 1/T
• What is peak current (I)?

  The maximum value of alternating current
• How can peak current or voltage be determined?

  From the amplitude of a current-time graph

  
• What does peak-to-peak current or voltage represent?

  The distance between positive and negative peaks

  
• How is peak voltage (V) calculated?

  Peak voltage = peak-to-peak voltage ÷ 2

  
• What does the graph of alternating current against time show?

  Time period, peak current, and peak-to-peak current

  
• What do root-mean-square (rms) values represent?

  Equivalent d.c. values producing same heating effect

  
• How is the rms value of an alternating current defined?

  Square root of the mean of the squares

  
• What is the equation for rms current (I_rms)?

  I_rms = $\sqrt{I^2}$