Module 4 - Chapter 10 - Electrical circuits Flashcards
What is Kirchhoff’s 2nd law?
In any circuit, the sum of the electromotive forces is equal to the sum of the p.d.s around a closed loop.
What is a series circuit?
A series circuit only has 1 path for the current to flow, a single loop.
What is a parallel circuit?
A parallel circuit has more than one path for the current to flow.
How would you find the total resistance of resistors in series with each other?
R = R₁ + R₂ + R₃ …
How would you find the total resistance of resistors in parallel with each other?
1/R = 1/R₁ + 1/R₂ + 1/R₃ …
once you get the sum of the right hand side, you might get a number like 5/33, for something like this you need to divide the 33 by the 5 to get the total resistance.
What is internal resistance?
Internal resistance is the resistance that any component has even if its not a resistor. Even components like batteries, lightbulbs, cells and power packs have an internal resistance.
What effect does internal resistance have on the p.d.?
The internal resistance means that not all the energy transferred to the charge goes into the circuit and is instead lost. This means that the terminal p.d. (the p.d. measured at the power sources terminals) is less than the actual e.m.f.. This is known as lost volts.
State the equation that links the e.m.f. to the terminal p.d.
e.m.f. = terminal p.d. + lost volts
How would you find the e.m.f.?
Connecting a high resistance digital voltmeter across the cell gives the approximate e.m.f..
Give the equations to find e.m.f.
ε = V + Ir
ε = IR + Ir
ε = I(R + r)
r is the internal resistance
R is the resistance of the circuit
What is a potential divider?
A potential divider is where 2 different resistors are used to vary the output p.d. from a fixed input p.d.
State the equation for potential dividers
Vout = (R₂ / R₁ +R₂) x Vin
What is a potentiometer?
A potentiometer is a variable resistor with 3 terminals and a sliding contact, it can be sued to easily change the resistance of the resistor and therefore the p.d. by just moving the sliding contact.
