Kirchoff's Laws and circuits Flashcards
What is Kirchhoff’s Second law?
The sum of the emf = sum of the pd’s around a closed loop.
Is the current the same at all points in a series circuit?
Yes, because of Kirchhoff’s 1st law
Is the voltage the same at all points in the series circuit?
No, the sum of the pds across each component adds up to the emf. Pd is shared.
How is emf shared across each component if they have different resistances?
The component with the larger resistance will take a greater proportion of the emf.
Is current the same at all points in a parallel circuit?
No, because of Kirchhoff’s 1st law so how much charge flows through each loop depends on the resistance of that path.
Is pd the same at all points in a parallel circuit?
Yes, because of Kirchhoff’s 2nd law. If one branch contains several components, the sum of the pds will = the emf.
Why does adding resistors in series increase the resistance?
Because adding more resistors increases the L of the path taken by the charges.
Why does adding more resistors in a parallel circuit decrease the total R?
This is because the additional resistor adds another path for the charges, increasing the A.
What are lost volts?
When there is a current in a power source, work has to be done by the charges as they move through the power source so some energy is lost/transferred to heat. The pd measured at the terminals of the power source is less than the actual emf.
What is the relationship between emf and lost volts?
emf=terminal pd+lost volts
How does increasing the current change the lost volts?
Increases the lost volts as more work is done and more energy is lost.
What is the equation for lost volts?
lost volts = Ir
Is the emf value close to the pd value when the current is very small?
Yes
What does the gradient of a VI graph give?
-r (V=-rI+epsilon)
What are potential divider circuits?
Can vary the pd across an output when connected to a fixed input.
