Chapter 9: Energy, Power and Resistance Flashcards
What is the definition of the Volt?
The Volt is defined as the amount of energy transferred per unit charge when it passes through a component.
One Volt is 1 Joule of Energy transferred per Unit Charge when it passes through a component.
What is the definition of Electromotive force, and its equation?
Electromotive Force is defined as the energy transferred from Chemical Energy (or other forms of energy) into Electrical Energy per unit Charge.
The Equation for emf is: V = W / Q
What is the definition of Potential Difference?
Potential Difference is defined as the energy transferred from Electrical Energy to other forms of energy per unit Charge.
The Equation for p.d. is: V = W / Q
What is the SI Units of the Volt?
The SI Units of the Volt are Joules per Coulomb, or J C-1
How are Voltmeters connected, and why do they have a high resistance?
Th Voltmeter is connected in parallel to the component it is measuring, and contains a very high resistance so that it will not affect the current (or p.d.) flowing through the component.
How do you calculate the amount of energy transferred when given the PD / EMF and Charge?
The equation to calculate work done / energy transferred with PD/EMF and Charge is:
W = VQ
What is Thermionic Emission?
Thermionic Emission is defined as the emission of electrons (or other charge carriers) from the surface of a metal due to heat when electrons gain enough kinetic energy.
How does the Electron Gun work?
The Electron gun consists of a small metal filament which acts as a Cathode for negatively charged electrons.
The filament is then heated up through an electric current which causes the filament to release electrons through thermionic emission.
The Heated Filament is then placed into a Vacuum and an accelerating p.d. is placed in between the Cathode and an Anode .
The Anode contains a small hole which allows electrons to pass through it.
Due to the Anode being positively charged and an accelerating p.d. between the two electrodes (filament and anode), the Electrons will accelerate towards the anode with an increase in kinetic energy and pass through the hole, creating a beam of electrons.
What is the equation to calculate the work done / energy transferred on an electron within an electron gun?
The work done (or energy transferred) on an Electron is equal to the gain of potential energy before it passes through the Anode.
The Equation to calculate this is:
eV = 1/2 mv²
*Where eV (or Ve) is the work done instead of VQ, the elementary charge is substituted instead of Q.
How does the accelerating p.d. affect the Kinetic Energy of the electrons?
A higher accelerating p.d. will lead to a higher gain in Kinetic Energy for the electrons which leads to the electrons travelling at a higher speed.
What is the definition of Resistance, and its equation?
Resistance is defined as a measure of difficulty of allowing current to flow through a component, or the potential difference of a component over a given current.
What is the definition of the Ohm?
An Ohm is defined as the resistance of a component when a p.d. of 1 Volt is produced per 1 Amp of Current. The SI Unit of an Ohm is V A-1
What is the cause of Resistance within components?
Resistance is caused due to the collision of electrons with the positive ions within the wire or component. As more electrons collide with the positive ions within the component, more work is done (or energy is transferred) from the electrons to the positive ions instead of the component. Materials with a higher resistance will contain more positive ions within them.
Why does Temperature affect Resistance?
Temperature affects resistance due to the rate at which the positive ions vibrate at within the metal. A higher temperature would lead to a greater increase in internal energy within the positive ions, leading to the positive ions vibrating at a greater amplitude within their mean positions. This will lead to a higher frequency of electrons colliding with the positive ions, therefore more work is being done within the wire and more energy (in the form of heat) gets transferred instead of its component.
What is the gradient on an I-V Graph?
The Gradient of an I-V Graph represents the inverse of resistance (1 / R). You can get the resistance by doing the reciprocal of the Gradient.
What is Ohm’s Law?
Ohm’s Law states that the current of a wire (or component) is directly proportional to the potential difference across its ends given that temperature remains constant.
What is the shape of an I-V Graph of a Resistor, and what does this shape mean?
The shape of an I-V Graph of a Resistor is a straight line gradient.
This means that the resistor is an Ohmic Conductor and its Resistance stays constant regardless of polarity.
What does a steeper gradient on an I-V Graph represent?
A steeper gradient on an I-V Graph represents a lower resistance.
What is the shape of an I-V Graph of a Filament Lamp, and what does this show?
The Shape of a Filament Lamp is initially a straight line which curves and decreases in gradient as Potential Difference increases. This is the same in both ways.
This shows that the Filament Lamp is a non-ohmic conductor and the resistance does not remain constant due to I not being proportional to V. This happens when temperature increases leading to a higher resistance.
What is a Diode?
A Diode is an electrical component that allows current to flow in one direction.
What is the shape of an I-V Graph of a Diode, and what does this show?
The shape of a graph of a Diode is a flat line in the negative direction. As the line crosses the origin in the positive direction, the line increases exponentially. This shows that current only flows in one direction, and resistance is not constant. Therefore, it is not an Ohmic Conductor.
What is the definition of the Threshold Voltage?
The Threshold Voltage is defined as the minimum potential difference needed in order for a Diode to conduct. After this voltage, the resistance decreases exponentially.
What Factors affect Resistance of a wire?
Factors that affect the Resistance of a Wire include:
- The Material of the wire
- The Length of the wire
- The Resistivity of the wire
What is the equation that links Resistivity, Resistance, Cross-sectional area, and Length of wire?
The equation that links Resistivity, Resistance, Cross-sectional area and Length of wire is:
p = RA / L (given that temperature remains constant)
What is the gradient of a Resistance - Length Graph?
The Gradient of a Resistance - Length Graph is:
p / A (Resistivity / Cross-sectional Area)
What is the meaning of a ‘Negative Temperature Coefficient’, and how does this happen?
A Negative Temperature Coefficient is a term that describes the decrease in resistance of a component as its temperature increases. This happens when the number density of the material increases as the temperature increases.
What are uses of a Thermistor?
Uses of a Thermistor include Thermostats, Thermometers, and monitoring temperatures of electrical devices and engines.
What is the shape of a Resistance - Temperature Graph of a Thermistor?
The Resistance - Temperature Graph starts at a high resistance and decreases exponentially as temperature increases.
What is a Thermistor?
A Thermistor is an electrical component that is made up of a semiconductor and has a negative temperature coefficient.
What is the shape of an I - V Graph of a Thermistor?
The Shape of an I-V Graph of a Thermistor is an exponential increase from the origin in a positive direction and a negative increase in the negative direction.
What is an LDR?
An LDR is a Light-dependant Resistor where its resistance depends on the incident light intensity. As light increases, the semiconductor increases in number density leading to an exponential decrease in resistance.
What is the definition of Power, and its Unit?
Power is defined as the work done (or energy transferred) over time. The unit of Power is the Watt (W).
What are the 3 Equations that link Power, Current, Resistance and Potential Difference?
The 3 Equations that link Power, Current, Resistance and Potential Difference are:
P = I x V
P = I² x R
P = V² / R
What are Kilowatt Hours (kWh) a unit of, and how is it calculated?
Kilowatt Hours are a unit of energy and can be calculated by doing:
W (J) = Power (kW) x Time (h). This is a unit of energy derived from Work = Power x Time.
What is the equation that links Power, Work Done and Time?
The Equation that links Power, Work Done and Time is:
Power = Work Done / Time
