circuit diagrams

1) Symbols for common Circuit Components

series and parallel circuits

2) Calculations
  • The current at any point in a series circuit is the same. 
  • The current splits at each branch in a parallel circuit so the total current is always greater than the current in one branch.
Combining Resistors:
  • In Series: 
Resistance:
\[R_{total}=R_{1}+R_{2}+R_{3}\]
Current: same current flows through every component.
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PD: PD total = sum of PD across each component.
  • In Parallel:
Resistance:
\[R_{total}=\frac{1}{\frac{1}{R_{1}}+\frac{1}{R_{2}}+\frac{1}{R_{3}}}\]
Current: current total = sum of current across each component.
​
PD: same PD across every branch.
The combined resistance of 2 resistors in parallel is less than that of either resistor by itself.
Advantages of putting lamps in parallel:
  • If one lamp breaks, the others still works.
  • Each lamp gets maximum PD.
3) Describe use of NTC thermistors and LDRs as input transducers
Transducers are devices that transform energy from one form to another.

Input transducers are transducers that change non-electrical energy to electrical energy. Examples:
  • NTC Thermistors: Negative Temperature Coefficient (NTC) thermistors are temperature dependent resistors. Their resistance reduces with increasing temperature.
  • Light dependent resistor (LDR): input sensor and a transducer. When light intensity increases, resistance decreases.
4) Electrical Energy
  • Electrical energy is transferred from the battery or power source to the circuit components then into the surroundings​.
  • 1 Watt is 1J/s
Electrical power (W) = Voltage (V) x Current (A)
P = V I
\[Electrical\: energy=\frac{Voltage}{Current}\]
\[E=\frac{V}{I}\]
5) Dangers of Electricity
Hazards:
  • Damaged insulation: contact with the wire (live wire especially) due to gap in the insulation causes electric shock which can cause serious injury or shock.
  • Overheating of cables: when long extension leads are coiled up, they may overheat. The current warms the wire, but the heat has less area to escape from a tight bundle. This might cause a fire.
  • Damp conditions: water can conduct a current, so if electrical equipment is wet someone might get electrocuted.
6) How a Fuse protect a Circuit
  • Thin piece of wire which overheats and melts if current is too high.
  • It is placed on the live wire before the switch. This prevents overheating and catching fire.
  • A fuse will have a specific current value (e.g. 13 Amps.) so when choosing a suitable fuse you must use the one above minimum value but less than maximum value
7) How a Circuit Breaker protect
An automatic switch which if current rises over a specified value, the electromagnet pulls the contacts apart, breaking the circuit. The reset button is to rest everything. It works like a fuse but is better because it can be reset.