4.3
electric circuits
4.3.1 circuit diagrams and circuit components
4.3.2 series and parallel circuits
series circuits
components are connected in a single loop.
- current is the same at all points
- potential difference is shared
- total resistance increases
rtotal = r1 + r2
parallel circuits
components are connected on separate branches.
- potential difference is the same across each branch
- current splits between branches
- total current is the sum of branch currents
itotal = i1 + i2
advantages of parallel circuits:
- full p.d. across each component
- independent operation
4.3.3 action and use of circuit components
resistors in parallel
total resistance decreases when resistors are connected in parallel.
1 / rtotal = 1 / r1 + 1 / r2
potential divider
two resistors in series can be used to divide potential difference.
v1 / v2 = r1 / r2
diodes and sensors
- diodes allow current in one direction only
- leds emit light when current flows forward
- thermistors increase resistance as temperature falls
- ldrs increase resistance as light intensity falls