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:
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Current: same current flows through every component.
PD: PD total = sum of PD across each component. |
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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:
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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:
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
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.