3.8 Power Flashcards
Define energy in the context of physics.
Energy is the capacity to do work or transfer heat.
What are the two main types of energy?
- Kinetic energy
- Potential energy
What is kinetic energy?
The energy stored in a moving body, transferred during its acceleration.
What is potential energy?
The energy stored by a system which may later be transferred to another energy store.
List examples of potential energy stores.
- Gravitational potential energy
- Elastic potential energy
- Electrical potential energy
- Chemical potential energy
What is the definition of work in mechanical systems?
A measure of the energy transferred when a force is applied over a distance.
How is work done measured?
In joules (J).
What is one joule equivalent to in terms of force and distance?
One joule is the work done when a force of one newton moves a mass over one metre.
In electrical systems, how is work defined?
The energy transferred when an electric charge is moved between two points in a circuit.
What unit is used to measure potential difference?
Volts (V).
Fill in the blank: Power is the rate at which _______ is done or heat is transferred.
work
What is the unit of power?
Watts (W) or joules per second (J/s).
How is electrical power defined?
The number of joules of energy transferred to or from a circuit in one second.
What is the difference between direct and indirect measurement of electrical power?
- Direct measurement: Using a wattmeter
- Indirect measurement: Using a voltmeter and an ammeter
What is the function of a voltmeter?
To measure potential difference across components in parallel.
What is the function of an ammeter?
To measure current in series.
True or False: Power remains constant over time for AC devices.
False
What does potential difference measure?
The electrical potential energy available per coulomb of charge.
What happens when a current flows through a resistor?
Energy is transferred from the electric circuit to the thermal energy store of the resistor
What is the work done by the electric circuit in relation to a resistor?
Transferring energy to the resistor and increasing the resistor’s temperature
How does heat flow from a resistor to the surroundings?
Through conduction, convection, and radiation
What happens to the heat generated by all components in a circuit?
It is dissipated into the air around the components
What is the rate at which heat is dissipated called?
Power, measured in watts (W)
True or False: Resistors are designed to dissipate power.
True
What limits the maximum power that a particular resistor can dissipate?
The resistor’s design and specifications
What can happen if the power dissipated exceeds the resistor’s limit?
- The value of the resistor may rise beyond its stated tolerance
- The resistor may melt (burn out and fuse)
- The resistor may start a fire
Why is it important to observe the correct power rating when designing circuits?
To ensure the circuit functions correctly and to prevent hazards
Fill in the blank: The heat generated by a resistor flows to the surroundings through _______.
conduction, convection, and radiation
What is electric power?
The rate at which work is done or energy is transformed into an electrical circuit
What is the formula for electric power?
P = VI
In the formula P = VI, what does P represent?
Power in watts (W)
In the formula P = VI, what does V represent?
Potential difference in volts (V)
In the formula P = VI, what does I represent?
Electric current in amperes (A)
What is the power consumption when the current is 1 ampere and the voltage is 1 volt?
1 watt
If a hydraulic pump has a voltage of 230 V and a current of 4 A, what is its power consumption?
920 W
Fill in the blank: Power is the product of _______ and _______.
voltage, current
True or False: The unit of power is measured in watts.
True
What is the relationship between voltage, current, and power?
Power is calculated by multiplying voltage and current
What is electrical power (P)?
The rate at which work is done or the rate of conversion of energy by an electrical system.
Power can also be expressed in terms of voltage and current.
What is the formula for power?
Power = work done (joules) / time taken (seconds).
This relationship shows how power relates to work and time.
What is the SI unit of power?
Watt (W), which is defined as 1 joule per second.
The watt is a measure of electrical power.
How can electrical power be expressed using voltage and current?
P = V x I
This expression is derived from Ohm’s Law where V = IR.
What happens to power if voltage is halved?
Only a quarter of the power is obtained.
This is due to the relationship P ∝ V².
What happens to power if voltage is doubled?
The power is four times larger.
This follows the same principle of P ∝ V².
How can power be calculated if resistance is known?
P = I²R or P = V²/R
These formulas allow calculation of power without direct current measurement.
What is electrical work?
Work done when a charge is moved between two points at different electrical potentials.
The formula for electrical work is W = Q x V.
What is the SI unit of work?
Joule (J).
One joule of work is done when one coulomb moves through a potential difference of one volt.
What is the formula for electrical work?
Electrical Work (joule) = Charge (coulomb) x Potential Difference (volt).
This shows the relationship between charge and electrical potential.
What is electrical energy?
The ability of an electrical system to do work.
Energy used is equal to the work done, with both measured in joules.
What does the Law of Conservation of Energy state?
Energy can neither be created nor destroyed but can be changed from one form to another.
This law emphasizes the transformation of energy rather than its disappearance.
What is the multiplier for the prefix ‘mega’?
1 000 000 (10^6).
Mega is commonly used in measuring large quantities.
How do you convert from low to high exponents in unit conversion?
Shift the decimal point to the left.
This method is essential for accurate unit conversions.
How do you convert from high to low exponents in unit conversion?
Shift the decimal point to the right.
This is the opposite action of converting from low to high exponents.
Fill in the blank: The energy a body contains may be determined by calculating the ______ done on the body.
work
This reflects the relationship between energy and work done.
What is the result of converting 125 microamperes to amperes?
0.000125 ampere.
This conversion illustrates the process of shifting the decimal point.
What is the result of converting 1 kW to watts?
1 000 W.
This demonstrates the conversion from kilowatts to watts by shifting the decimal point.
