POWER Flashcards
What is work in mechanical systems?
In mechanical systems, work is a measure of the energy transferred when a force is applied over a distance, or the potential of a system to do this work in the future.
What is the unit of work in mechanical systems?
Work done is measured in joules (J), where one joule is the amount of work done when a force of one newton (N) moves a mass over a distance of one metre (m) in the direction of the applied force.
What is the unit of work in electrical systems?
In electrical systems, work is a measure of the energy transferred when an electric charge is moved between two points in a circuit, or the potential for this charge to be moved in the future. Work done is measured in joules (J), where one joule is the amount of work done when a charge of one coulomb (C) is moved through a potential difference of one volt (V).
What is power?
Power is the rate at which either work is done or heat is transferred
What is rate?
A rate is simply the change in a quantity divided by the time taken for it to change, so power is measured in joules per second (J/s), which is also known as watts (W).
What is direct measurement?
Using a wattmeter (power meter): This is a special meter that consists of a voltmeter and an ammeter in one housing. It does the multiplying automatically; the indication is in watts. This is known as direct measurement.
What is indirect measurement?
Measuring voltage and current with a voltmeter and an ammeter: This involves taking two separate measurements and multiplying the results manually. This method of measuring is referred to as an indirect measurement of power.
How do you measure current?
Current is measured by an ammeter in series.
Explain power dissipation by a resistor?
When a current flows through a resistor, energy is transferred from the electric circuit to the thermal energy store of the resistor. Work is done by the electric circuit, transferring energy to the resistor and increasing the resistor’s temperature.
Due to the increased temperature of the resistor, heat flows to the surroundings through conduction, convection and radiation.
What may happen if a resistors power limit is exceeded?
The value of the resistor may rise beyond its stated tolerance, causing the circuit to malfunction.
The resistor may melt (burn out and fuse).
The resistor may start a fire.
What is the formula for power?
P=V TIMES I
What is the formula for Watts?
Watts = volts times amps
