Practical electricity Flashcards
(29 cards)
How to calculate power?
P=VI where;
P=power(watts)
V=voltage(volts)
I=current(ampere)
For a resistor with resistance R, the rate at which electrical energy is converted to thermal energy can be calculated using any if the following equations:
P=VI=I square R=V square/R
How to calculate electrical energy
E=VIt=I squareRt=V square/R x t
Calculating cost of electricity consumption
1 kWh= the energy consumed by a 1 kW device in 1 hour
Worked example 19.3
1.5 kW electric coil heats water for 2 hours. Calculate the amount of electrical energy consumed by the coil in a)kWh and b)J
a) energy = P x t
= 1.5 kW x 2h
=3.0 KWh
b) energy= p x t
= 1500 x 2 x 60 x 60
=10800000Renewable sources of energy( solar power)
Light energy———-> electrical energy
Efficiency:
- Higher efficiency when there is daylight and minimal cloud cover
- Excess energy generated can be stored or fed back to the power grid
Cost: High cost involved in manufacturing solar panels, but cost of fuel which is sunlight, is free
Environmental impact: A form of clean energy, but requires large areas to be cleared for solar panels to be installed
Renewable sources of energy( hydroelectric power)
Gravitational potential energy————> electrical energy
Efficiency: most efficient source of energy as the water flow is concentrated and can be easily controlled
Cost:
- High cost involved in constructing the dam and power plant
- Costs also involved in maintenance, as silt may build up behind the dam and block the water flow
Environmental impact:
A form of clean energy, but teh building if dams disrupts ecosystems
Renewable sources of energy ( wind power)
Kinetic energy————> electrical energy
Efficiency: efficiency varies, depending on wind direction and speed
Cost:
-cost of wind power is falling with improvement in technology
- Wind energy is free, therefore costs mainly go towards maintenance.
Environmental impact:
A firm of clean energy, but the spinning turbines produce some noise pollution and also require large open areas
Non renewable sources of energy (nuclear power)
Nuclear energy————>heat energy—————>electrical energy
Efficiency: High efficiency as a small amount of uranium is sufficient to generate a large quantity of energy
Cost: compared to other sources of energy, additional cost is involved in the disposal of radioactive waste
Environmental impact: waste from uranium mining can contaminate groundwater and surface water sources
Non renewable source of energy(fossil fuel)
Chemical potential energy———->heat energy———>electrical energy
Efficiency: most counties have well-established technology and energy distribution systems
Cost: cost is rising due to the declining supply of fossil fuels and the rising demand for energy
Environmental impact:
- extensive mining has a negative impact on the ecosystem around a mine
- Burning if fossil fuels results in air pollution
1) overloaded power sockets
When a power socket is overloaded with many appliances, an usually large current flows through the wires
Use of inappropriate wires
A thin wire has high resistance and hence generates large amounts of heat
Damp environment
Water in contact with the uninsulated wires provides a conducting path for current. As the human body can only withstand an alternating current of about 50mA, a large current will cause burns, uncoordinated contraction of the heart muscles, or even death
What are circuit breakers
Circuit breakers are safety devices that can switch off the electrical supply in a circuit when large currents flow through them.
What are circuit breakers connected to?
Circuit breakers are connected to live wires, so that should there be a current surge due to a fault, the circuit breakers will trip and cut off the current to the appliances. Thai ensures that the appliances are isolated from the mains, and the users do not get electric shocks
What is a fuse?
A fuse is a safety device added to an electrical circuit to prevent excessive current flow.
Difference between a fuse and a circuit breaker?
A fuse must be replaced after it blows, whereas a circuit breaker can be reset after it trips.
Why does a fuse consist of a thin wire?
The wire is made thin so that when a large current flows through it, it heats up and melts. When a fuse blows, a gap is created in the circuit. The circuit is opened, and current stops flowing through the circuit.
For safety reasons, the flowing points should be considered when selecting and installing fuses:
- The fuse if an electrical appliance should have a rated value that is slightly higher than the current the electrical appliance draws under normal operating conditions
- The fuse should be connected to the live wire so that the current to the appliance will be cut off immediately after a large current melts the fuse and will not be at a potential of 240V
- The mains power supply must be switched off before replacing a fuse
What are switches?
Switches are designed to break or complete an electric circuit
What happens when the switch is fitted to a neutral wire
1) An electrical fault results in the live wire touching the metal casing
2) As the switch is fitted to the neutral wire, the metal casing is still connected to the live wire when the switch is open. The metal casing is at high voltage.(240V)
3) If a person touches the emerald casing, a large current flows through the person to the earth- the person gets an electric shock
What happens if the switch is fitted to the live wire?
1) As the switch is fitted to the live wire, the metal casing is disconnected from the live wire when the switch is open. The metal casing is at Low voltage(almost 0V)
2) No current flows through the person touching teh casing
What is the live wire
The live wire(brown) is connected to a high voltage and delivers current to the appliance
What is the neutral wire
The neutral wire(blue) completes the circuit by providing a return path the supply for the current. It is usually at 0V
