3.6 DC Circuits Flashcards
What does Ohm’s law describe?
The relationship between current and voltage for most conductors
Who established Ohm’s law and when?
Georg Simon Ohm in 1827
What is the formula for Ohm’s law?
V = I * R
What do the symbols V, I, and R represent in Ohm’s law?
- V: voltage in volts (V)
- I: current in amperes (A)
- R: resistance in ohms (Ω)
What is resistance?
The quotient of voltage to current, measured in ohms (Ω)
What is the characteristic of materials obeying Ohm’s law regarding resistance?
Resistance does not change over enormous ranges of voltage and current at constant temperature
What is Kirchhoff’s 1st Law?
At any junction in an electrical circuit, the sum of currents flowing towards that point equals the sum of currents flowing away from it
What can Kirchhoff’s 1st Law be used to calculate?
Unknown currents at a branching point in an electrical circuit
What is Kirchhoff’s 2nd Law?
The algebraic sum of all voltages around any closed loop is zero
What does Kirchhoff’s Voltage Law imply about voltage in a circuit?
Voltage is dropped through components with none left over in a closed loop
True or False: Voltage exists at a single point in a circuit.
False
What year were Kirchhoff’s circuit laws first described?
1845
Who first described Kirchhoff’s circuit laws?
Gustav Kirchhoff
What is the significance of Kirchhoff’s laws?
They are essential tools for the analysis of electric circuits
What is Ohm’s Law used for?
To calculate an unknown value for either voltage, current, or resistance
Ohm’s Law is expressed as V = IR, where V is voltage, I is current, and R is resistance.
What does Kirchhoff’s 1st Law state?
The total current flowing towards a node is equal to the total current flowing away from the node
This is also known as Kirchhoff’s Current Law.
What is the principle behind Kirchhoff’s 2nd Law?
The total EMF must equal the total PD in a circuit
EMF stands for electromotive force and PD stands for potential difference.
How can unknown PD be calculated using Kirchhoff’s 2nd Law?
By subtracting the known PDs from the total EMF
This allows for the determination of unknown voltages in a circuit.
In a parallel circuit, what is true about the PD across resistors?
The same PD is across all resistors connected in parallel
This is important for accurate calculations of current through each resistor.
What is the voltage across the 6 Ω resistor in the example?
6 V
This voltage is the same as the voltage across the 12 Ω resistor due to their parallel connection.
How do you calculate the current through a resistor using Ohm’s Law?
I = V/R
I is current, V is voltage, and R is resistance.
What is the voltage across the 2 Ω resistor in the example?
3 V
This was calculated using Ohm’s Law after finding the current through the resistor.
What is the total EMF calculated in the example?
9 V
This is derived from the sum of the PDs across the resistors connected in the circuit.
Fill in the blank: According to Kirchhoff’s 1st Law, the total current at a node is equal to the total current _______.
flowing away from the node
True or False: Kirchhoff’s 2nd Law can be used to find unknown voltages in a circuit.
True
What does Internal Resistance (IR) refer to in a power supply?
A small resistor in series with the pure EMF of a power source
This resistance influences the terminal voltage depending on the current supplied.
What is the terminal voltage of a power supply when it is off-load?
The terminal voltage is equal to the EMF
This occurs when no current flows through the internal resistance.
What happens to the terminal voltage when the power supply is on-load?
The terminal voltage decreases compared to the EMF
This is due to the potential difference (PD) across the internal resistance.
How is terminal voltage calculated when a power supply is on-load?
Terminal voltage = EMF - PD across internal resistance
The PD increases with higher current.
What is the effect of a short-circuit on a power supply’s current?
A high current flows, limited only by the IR of the battery
This can lead to dangerously high short-circuit currents.
What can excessive short-circuit current do to a power source?
It can quickly destroy the power source
Many power supplies have low IR, leading to high short-circuit currents.
What factors contribute to achieving a stable terminal voltage in a power supply?
Choice and combination of power sources, voltage regulators, and load resistors
These components help maintain constant voltage and current.
How is a battery’s Internal Resistance (IR) calculated?
IR = (Open-Circuit Voltage - Closed-Circuit Voltage) / Load Current
IR increases as the battery discharges.
What is the typical IR of an AA battery cell?
About 0.1 Ω
This value affects the voltage between the terminals depending on the current.
What is the danger associated with larger power sources compared to smaller ones?
Larger power sources can be potentially fatal
For example, a 20 V and 200 A source is much more dangerous than a small dry cell.
What should users be cautious about regarding the ratings on batteries?
The terminal voltage and maximum current ratings
These ratings help prevent mishandling and dangerous situations.
True or False: The terminal voltage of a power supply is always the same as its EMF.
False
The terminal voltage can be lower than the EMF when on-load.
Fill in the blank: The actual voltage across the terminals of a power supply is called the _______.
terminal voltage
It varies based on the current supplied to an external load.
