Energy, Power and Resistance Flashcards
What is a Volt
The Potential difference across a components when one Joule of energy is transferred per unit charge passing through the component,
What is potential difference
The energy transferred from electrical energy to other forms per unit charge. Describes when work is done by charge carriers, losing energy as they pass by components.
What is Electromotive force
The work done on charge carriers. Charge carriers gain energy as they pass through batteries or cells. Defined as the energy transferred from chemical to electrical energy per unit charge
How does an electron gun work
A metal filament in a vacuum is heated by an electric current, increasing the kinetic energy of electrons in the filament. This causes some electrons to escape the filament. A potential difference is applied to the filament and an anode, causing the filament to act as a cathode, and accelerating the freed electrons towards the anode. A small hole in the anode allows the electrons to pass through it, creating a beam of electrons.
What is the resistance of a component defined as
The ratio between V and I
What is Ohms law
P.d and Current are directly proportional for a metallic conductor kept at a constant temperature.
What happens to the current of a circuit when temperature increases
The current decreases, due to the fact that the increased temperature increases the kinetic energy of positive ions, causing them to vibrate with greater amplitude. This increases the collisions between free electrons and positive ions, requiring greater work done by the electrons to travel through.
Things to consider with I-V characteristics
Is it an Ohmic component? If straight line through origin, then yes, If not, then no.
Does it behave the same way regardless of polarity? Shown by a same line in the negative quadrant.
Is the resistance constant? Shows by a constant gradient.
How does a filament lamp work
Electrons collide with the positive ions in the filament, transferring energy to them. This causes them to vibrate with a greater amplitude, increasing temperature and causing the filament to glow. This causes an increase in resistance in the lamp, as the electrons require more work to travel through it due to a greater number of collisions.
What is a diode
A component that only allows current to move in one direction. The I-V characteristics are that it is a non ohmic component, the resistance is not constant and its behaviour depends on the polarity of the cell/battery. Diodes have threshold Potential differences which once passed causes the resistance to drastically decrease.
What 4 things affect resistance
Temperature, Material, Length and Cross sectional area. Resistance is directly proportional to length. Inversely proportional to area.
What is resistivity
A quantity that defines a materials ability to resist the flow of current. Varies with temperature similar to resistance.
What is Superconductivity
When a material is cooled, and has a resistivity of 0 at a critical temperature. No energy is lost as current travels through the material.
What is a thermistor
An electrical component made from a semi conductor whose resistance is inversely proportional to temperature. Its I-V characteristics are that the resistance decreases as current increases. As current increases, temperature increases, increasing the number density of free electrons due to thermal excitation of atoms.
Thermistor experiment
Connect the thermistor to an ammeter and voltmeter. Place thermistor in a water bath, alongside a thermometer. Increase temperature and record change in Current and P.D. Plot graph of I against V
