Electric Fields Flashcards
(28 cards)
What is the definition of electric potential?
Energy per unit positive charge in moving from infinity to a given point in an electric field.
Electric potential is measured in volts.
What is electric field strength?
Force per unit charge (N C⁻¹)
Electric field strength is also measured in volts per meter (Vm⁻¹).
What is a test charge?
A positive charge with a magnitude so small that it has no effect on the field
What do the direction of electric field lines indicate?
The path followed by a positive test charge
From where to where do electric field lines go?
From positive to negative
State Coulomb’s law in words
The force between two charges is directly proportional to the product of the two charges and inversely proportional to their separation squared
How is a uniform electric field respresented in diagrams?
Parallel field lines that are equidistant from one another
What is a cathode ray tube (CRT)?
A device that releases electrons from a hot filament via thermionic emission and directs them using electric fields
Why must a cathode ray tube operate in a vacuum?
To prevent electrons from interacting with anything before reaching the screen
What is thermionic emission?
Emission of electrons from a hot filament
What is a capacitor?
A capacitor is basically just two metal plates, positioned closely, but not touching, and usually separated by an insulator, known as a dielectric.
What is capacitance?
Charge stored per unit volt
In what unit is capacitance measured?
Farads (F)
What is the relationship between charge and voltage in a capacitor?
The higher the voltage, the more charge can be stored.
What happens when a capacitor is connected to a cell?
The plate connected to the negative terminal collects electrons and becomes negatively charged, while the positive plate becomes positively charged.
What occurs to the current as a capacitor charges?
The current decreases as the charge on the plates builds up
When does the current stop flowing in a charging capacitor?
When the potential difference across the capacitor equals the potential difference across the cell
What is the discharge rate of a capacitor?
The initial discharge rate is high but decreases as it loses charge
What does the curve of voltage/current/charge over time look like during discharge?
It is an exponential decay
What is the time constant?
The time it takes for a capacitor to fall to 1/e (about 37%) of its initial voltage.
What percentage of energy does a capacitor store in a DC circuit?
A capacitor will only store 50% of the energy expended by the cell.
Capacitors in series store..
equal charge
What is permittivity?
The ability of a substance to store energy in an electric field
What is the value of the permittivity of free space?
The ability of a vacuum to store energy in an electric field
