Chapter 19 - Practical Electricity Flashcards
What is the Symbol for Power
P
P = ? (Voltage and Current)
V x I
P = ? (Resistance and Current)
I x I x R
P = ? (Resistance and Voltage)
V x V / R
S.I Unit for Power?
Watt
An electrical appliance has a power of 1000W, what does it mean?
That means i convert/use 1000J of electrical energy in one second
What is the symbol for energy?
E
What is the S.I Unit for energy?
Joule (J)
E = ? (Power and Time)
P x t
Cost of electrical energy used = ?
Number of kWh used x Cost per kWh, the unit kWh is commonly used to calculate the cost of electricity.
What does 1 kWh means?
1000 Watt of power used in 1 hour
In a three pin plug, which are the positions of the Live, Neutral and Earth wires?
Earth: Top
Live: Right
Neutral; Left
What is the purpose of using a double switch?
To allow the user to control the current flow from two different places, eg. opposite ends of corridor
All switches/fuses must be connected to the live wire not the neutral wire. Why?
If the switch/fuse is connect to the neutral wire, when the switch is open/the fuse is melted, the live wire is still connected to the appliance. Thus, current can still flow through appliance, the metal casing of the appliance remain ‘live’, and if people touch the appliance, they will get electrocuted
What are the 5 safety features that can be found in our homes which prevent electrical hazards from occurring?
Circuit Breaker Earthing/Earth Wire Fuses Double Insulation Switches
What is purpose of inserting a fuse into an electrical appliance?
To protect the equipment and wires from EXCESSIVE current flow
How does a fuse work to prevent excessive current flow?
Fuse has a very low melting point, when it is heated up due to excessive current flow, it will melt immediately and thus cut off the current.
If a circuit is designed to take 3A of current, what rating of fuse is suitable for the circuit?
4A or 5A fuse, the rating of the fuse should be just slightly higher than the current that the circuit is designed to take.
What is the colors of the earth, live and neutral wire respectively?
Earth:Green and yellow
Live: Brown
Neutral: Blue
How does the Miniature Circuit Breaker works to prevent electrical hazard?
When there is a short circuit or excessive current flow, the Miniature Circuit Breaker will ‘trip’ and cut off the electricity.
What is the advantage of Miniature Circuit Breaker over fuse?
Miniature Circuit Breaker can be reset to regain the electricity supply, however, a when a fuse is blown, it has to be replaced by another one.
Why an Earth wire is necessary for an electrical appliance?
Because sometimes the live wire might come loose and touch the metal casing of the appliance, and if we touch the metal casing, we will be electrocuted. If earth wire is installed, the current will be diverted to the earth instead and we will be safe to touch the metal casing.
The earth wire must always be connected to ?
The metal casing of the electrical appliance
What is symbol for double insulation?
回
What is the safety feature of the double insulation?
It offer double level of insulation. A insulation covering the live wire and the neutral wire. A outer casing complete made of plastic (non-conductor of electricity)
How does a electric shock happen?
The insulation of the wires may worn off over time. When the wires are exposed and the person touch the wire, the current will flow through the human body, thus the person will get a electric shock
How does a fire caused by wires happened at home?
The insulation of the wires may worn off over time. The live and neutral wire may touch each other and thus there will a short circuit which allows large current flow. A fire will happen due to overheating of wire or the plastic insulation
Why cables will get overheated?
Cables have their own current rating. Sometimes sockets are overloaded using extension plugs. When the current flowing exceeds the current rating, the overloaded cable will get overheated.
Why a DRY body touch a live wire will not get electrocuted?
The SKIN of the dry body has a very high resistance
What is the logic behind a test pen that allows the electrician to test the wire and identify if the wire is neutral or live wire without harming himself?
A test pen contain a high-resistance carbon conductor which allows small and harmless current to pass through the test pen and the human body from the live wire to the earth. When the current pass through, neon tube will light up to notify the electrician that the wire is a live wire.
What are three example and two examples for renewable and non-renewable source of energy respectively?
Renewable: Solar, wind and hydroelectric
Non-renewable: Fossil Fuel, Nuclear
What are the environmental impacts for solar, hydroelectric, wind, nuclear and fossil fuel energy?
Solar: Large area needed to be clear for solar panels
Hydroelectric: Construction of dams will disrupt ecosystem
Wind: turbines produce noise pollution and require large open areas
Fossil Fuel:Burning of fuel results in air pollution
Nuclear:Wastes from uranium mining will contaminate groundwater and surface water
