C13 | 전기 시스템 (Electrical Systems) Flashcards
Electrical Systems
What is an Electric Current and the SI Unit?
An electric current is the rate of electric charge.
Système International Unite: Ampere (A)
What is Conventional Current?
In a closed electric circuit, current flows from the positive terminal of a battery to the negative terminal. This is Conventional Current.
What is Electron Flow?
After the discovery of electrons, it became known that electron flow occurs from the negative to the positive terminal. The direction of conventional current flow is opposite to the direction of electron flow.
What is the instrument used to measure current?
Ammeter
It must be connected in series.
What is Potential Difference and the SI Unit?
The potential difference between any two points is the amount of energy needed to move one unit of electric charge from one point to another.
Système International Unite: Volt (V)
What is the instrument used to measure Potential Difference?
Voltmeter
The voltmeter must be connected in parallel to the circuit component.
What is Resistance and the SI Unit?
The resistance of a component is the ratio of the potential difference across it to the current flowing through it.
Système International Unite: Ohm (Ω)
What is the Resistance Value of a Fixed Resistor and the Effect on Current?
Resistance Value: Fixed
Effect on Current: Cannot vary the amount of current flow in a circuit.
What is the Resistance Value of a Variable Resistor and the Effect on Current?
Resistance Value: Variable
Effect on Current: Can vary the amount of current flow in a circuit.
When you add a Variable Resistor in a Parallel Circuit, how does it affect the circuit?
Hint: Resistance Value, Current: How high or low, Brightness
Adding in another Variable Resistor in a Parallel Circuit decreases the resistance in the circuit. Hence, the current flowing through the light bulb increases. The light bulb becomes brighter.
When you add a Variable Resistor in a Series Circuit, how does it affect the circuit?
Adding in another Variable Resistor in a Parallel Circuit increases the resistance in the circuit. Hence, the current flowing through the light bulb decreases. The light bulb becomes dimmer.
When a Rheostat (Variable Resistor) slider is on the left, what is the effect on the circuit?
Hint: Resistance Value, Current Flowing, Brightness
When the slider is on the left, the short resistance wire offers low resistance. The current flowing through the circuit is large. Hence, the light bulb lights up brightly.
When a Rheostat (Variable Resistor) slider is on the right, what is the effect on the circuit?
Hint: Resistance Value, Current Flowing, Brightness
When the slider is on the right, the short resistance wire offers high resistance. The current flowing through the circuit is smaller. Hence, the light bulb is dimmer.
What does V, I and R stand for in the formula triangle?
V: Potential Difference
I: Current
R: Resistance
How is the formula VIR arranged in a triangle?
V on the top.
I & R on the bottom.
What are some effects of an Electric Current?
- Chemical Effect
- Magnetic Effect
- Heating Effect
What are the two types of Chemical Effects?
Electrolysis
Electroplating
What is Electrolysis?
- Electrolysis is a process that uses electricity to break down or decompose compounds.
- For example, aluminium can be obtained from bauxite by passing electricity through molten bauxite. Bauxite is a raw material that contains aluminium.
What is Electroplating?
- Electroplating is used to coat objects with metals by immersing the object in a liquid and then passing an electric current through the liquid.
- When a current runs through the solution, the metal electrode will decrease in mass, and the metal is deposited evenly on the object to be electroplated.
What are some hazards of electricity?
- Electrical Fire
- Electrocution
What are three safety features to deal with large currents?
- Earth Wire
- Fuse
- Circuit Breaker
What are the three types of electrical wires?
- Neutral Wire
- Earth Wire
- Live Wire
What colour is the Neutral, Earth and Live Wire?
Neutral: Blue
Earth: Yellow & Green
Live: Brown
Describe the Live Wire.
Describe: Colour, Voltage, Current Absent/Present
- Brown Colour
- Has a voltage of 240V
- Current is present when appliance is working normally.
Describe the Neutral Wire.
Describe: Colour, Voltage, Current Absent/Present, Function (Optional)
- Blue Colour
- Has a voltage of 0V
- Current is present when appliance is working normally.
- The Neutral Wire conducts electricity from the appliance back to the mains supply. The current is supplied to the homes through the live wire and returns to the substation through the neutral wire.
Describe the Earth Wire.
Describe: Colour, Voltage, Current Absent/Present
- Yellow & Green Colour
- Has a voltage of 0V
- No current flow when appliance is working normally.
- Only carries current when the appliance is faulty.
- Connected to the ground or earth.
- The Earth Wire is connected between the metal casing of the electrical appliances and the ground or earth.
Describe what happens if the earth wire is absent and VS it being present.
Absent
* When the earth wire is absent, an excessive flow of current through the metal casing of the electrical appliance can cause the user to be electrocuted upon touching it.
Present
* When the earth wire is present, the user is protected from an electric shock, as it conducts the current from the metal casing to the ground.
When drawing the Live, Earth, and Neutral Wire, where must the switch and fuse be located at?
It must be at the line of the Live Wire.
How does the Earth Wire prevent electrocution?
- If the appliance is faulty, the live wire touches the metal casing.
- This causes current to flow to the metal casing.
- By earthing the metal casing, any excess current will be sent to the ground by the Earth Wire.
- This prevents the user from getting an electrocution when touching the faulty appliance.
How does the fuse prevent excessive current to flow?
- When there is a large current, the short and thin wire in the fuse heats up and melts. The fuse is then said to be “blown”.
- This shuts off the current and protects the elctrical appliance from overheating. The blown fuse needs to be replaced after the electrical fault has been rectified.
- The fuse will be labelled with the current that will melt the wire in it. Eg. (1A, 2A, 3A)
- Since the fuse is connected to the live wire and when it melts, it will prevent current from flowing through. Henceforth shutting down the entire current.
If we select a fuse with a rating significantly higher than the current when the appliance is functioning normally, what will happen?
The higher the fuse rating, the higher the risk the circuit poses, as it allows more current to flow before the wire inside the fuse melts.
What is the function of the Circuit Breaker?
A circuit breaker monitors and limits the amount of current flow through the electrical wiring in the household circuits.
- What wire is the circuit breaker connected to?
- Does it need to be replaced after it shuts off?
- Where can the circuit breaker be found?
- The circuit breaker is connected to the live wire and cuts off an electric current when a large current is flowing through.
- No, it does not need to be replaced after it shuts off.
- It can be found in the consumer unit, where each circuit breaker is a switch-like lever connected to a different part of the household circuit.
* Once the damaged appliance or damaged part of the circuit is fixed, the circuit may be switched on again using the circuit breaker.
Define Power and the SI Unit.
- Power is defined as the amount of electrical energy converted to other forms of energy per unit time by the component.
- Système International Unite: Watt (W)
- 1000W = 1kW
What is the formula for Energy, Power, and Time?
Top of Triangle: Energy
Bottom of Triangle: Power & Time
수학 문제
If an oven toaster has a power rating of 1.8kW and it is being used for 2.5 hours, find
(a) Energy Used (kWh)
(b) Cost, if 1kWh of electrical energy costs $0.28 ($)
계산기를 사용해 주세요.
(a) Energy = Power X Time
E: 1.8 X 2.5 = 4.5kWh
(b) Cost = $0.28 X 4.5kWh
= $1.26
수학 문제
If a vacuum cleaner has a power rating of 750W and it is being used for 28 mins, find
(a) Energy Used (kWh)
(b) Cost, if 1kWh of electrical energy costs $0.28 ($)
계산기를 사용해 주세요.
(a) Energy = Power X Time
E: 750/1000 (Out of 1kWh) X 28/60 (Out of 1 hour) = 0.35kWh
(b) Cost = $0.28 X 0.35Wh
= $0.098
OR
= $0.10
