electricity - types of current

Question 1

direct current

Answer 1

in direct current (DC) circuits, the current flows around in one direction, from negative to positive
this is the type of current that flows in circuits powered by batteries and solar cells
(originally scientists believed in conventional current, from positive to negative however they discovered electrons have a -ve charge)

Question 2

alternating current

Answer 2

in alternating current (AC) circuits, the current flows both ways, charging direction regularly
this is the type of current that flows in mains electricity circuits, and from generators
in the UK, our mains electricity has a frequency of 50Hz and a peak voltage of 230V

Question 3

what is an oscilloscope

Answer 3

a piece of apparatus that can be used to measure the voltage and frequency of an alternating current

a DC supply will show a horizontal trace because current flows in one direction

an AC supply will show a wave because voltage is constantly changing direction

Question 4

the y-sensitivity setting

Answer 4

to calculate the voltage: multiply amplitude by y-sensitivity setting

increasing the y-sensitivity dial will increase the range of the oscilloscope but will decrease precision - you should aim to make the trace fit on the screen and as clear as possible (1 wave cycle at least)

Question 5

peak voltage and time base dial

Answer 5

as the size of the voltage is always changing, you would measure the peak voltage (amplitude x y-sensitivity setting)

the time base dial is used to adjust the wavelength of the displayed wave - increasing the setting will squash the wave to fit more cycles on the screen

Question 6

measuring frequency

Answer 6

you cannot measure frequency but you can measure the time period and use it to calculate frequency

time period is calculated by multiplying the wavelength of the wave (distance between corresponding points) by the time-base setting
–> this tells you how long 1 cycle will take in milliseconds

frequency = 1/time period