elec Flashcards
What is electric current (I)?
The flow of charge per unit time, or the rate of flow of charge
Electric current is measured in amperes (A)
Define potential difference (V).
The energy transferred per unit charge between two points in a circuit
Measured in volts (V)
What does Ohm’s law state?
For an ohmic conductor, current is directly proportional to the potential difference across it, given that physical conditions are kept constant
Expressed as V = IR
Describe the current-voltage graph of an ohmic conductor.
It looks like a straight line through the origin
This holds true as long as physical conditions such as temperature remain constant
What is the behavior of a semiconductor diode in forward bias?
Allows current to flow easily past the threshold voltage
The threshold voltage is the smallest voltage needed to allow current to flow
What happens to the resistance of a metal conductor as temperature increases?
The resistance increases
Due to increased atomic movement causing more collisions with charge carriers
How does a filament lamp behave as current increases?
Its resistance increases as the current increases
The graph begins to curve due to increasing resistance
What is resistivity (ρ)?
A measure of how easily a material conducts electricity, defined as the product of resistance and cross-sectional area, divided by the length of the material
Resistivity is dependent on environmental factors, such as temperature
What are the rules for adding resistances in series?
RT = R1 + R2 + R3 + …
Where RT is the total resistance and Rn is the resistance of resistor n
What are the rules for adding resistances in parallel?
1/R_T = 1/R_1 + 1/R_2 + 1/R_3 + …
This shows that the total resistance in parallel is less than any individual resistor
What occurs to the resistance of a thermistor as temperature increases?
The resistance decreases
This is due to an increase in charge carriers as electrons are emitted from atoms
What is a superconductor?
A material that has zero resistivity below a certain temperature known as the critical temperature
Most known superconductors operate close to 0 K (-273°C)
List two applications of superconductors.
- Power cables that reduce energy loss through heating
- Maglev trains that utilize strong magnetic fields
Applications also include certain medical technologies
What is the relationship between power (P), energy (E), and time (t)?
P = E/t
Power is the rate of energy transfer
What is the formula for calculating the energy transferred by a device?
E = Pt
Where P is power and t is time
What is electromotive force (emf)?
The energy transferred by a cell per coulomb of charge that passes through it
Represented as ε
What is internal resistance (r) in a battery?
Resistance caused by electrons colliding with atoms inside the battery
This leads to energy loss before electrons leave the battery
What is a potential divider?
A circuit with several resistors in series connected across a voltage source to produce a required fraction of the source potential difference
It can supply a variable potential difference using a variable resistor
In a series circuit, how is the total voltage calculated?
V_T = V_1 + V_2 + V_3
The total voltage is the sum of the individual voltages of the cells
In a parallel circuit, how is the total voltage calculated?
V_T = V_1 = V_2 = V_3
The total voltage is equal to the voltage of one cell
True or False: Charge and energy are always conserved in DC circuits.
True
Kirchoff’s laws describe how this conservation occurs
What does Kirchoff’s first law state?
The total current flowing into a junction is equal to the current flowing out
This shows that no charge is lost at any point in the circuit
What does Kirchoff’s second law state?
The sum of all the voltages in a series circuit is equal to the battery voltage
This shows that no energy is lost at any point in a circuit
What is the terminal potential difference (V)?
The potential difference across the resistor R
It is different from lost volts, which represents energy wasted by the cell per coulomb of charge
