Chapter 10 Electrical Circuits

Question 1

What is kirchoff’s second law?

Answer 1

The sum of the potential differences in a circuit is equal to the sum of the electromotive forces in a closed loop
ΣV = Σε

Question 2

What is a series circuit? What are its properties?

Answer 2

It is a circuit with only one path for the current to flow.
The currents are the same in every position
The emf is shared between all the components in the series circuit.

Question 3

What happens if we have multiple cells in a series circuit?

Answer 3

The EMF’s of each battery are added together to make a total EMF.

Question 4

What is a parallel circuit? What are its properties?

Answer 4

It is a circuit that allows more than one path for the current to travel. The amount of current is dependent on the resistance of each path, more resistance, more current.

Question 5

What is the rule about the potential differences in each branch of a parallel circuit?

Answer 5

The potential differences of all the components on each branch is equal to the EMF

Question 6

PRACTICE QUESTIONS ABOUT CIRCUITES

Answer 6

DO IT

Question 7

What is the equation for resistors in series?

Answer 7

Rt = R1 + R2 + R3 + Retc

They are simply added together

Question 8

What is the equation for resistors in parallel?

Answer 8

1/Rt = 1/R1 + 1/R2 + 1/R3 + 1/Retc

This is because resistors in parallel reduce the resistance

Question 9

What about the voltage can we determine from resistors in series?

Answer 9

The potential differences from all the resistors can be added together to get the overall potential difference

Question 10

What are the 4 most important electrical equations?

Answer 10

I = Q / T
V = W / Q
P = VI
V = IR

Question 11

If a large current is needed, what is the internal resistance that is required?

Answer 11

A low internal resistance

Question 12

What is internal resistance?

Answer 12

Whenever there is a current in a power source, work has to be done to move the charges so there is an internal resistance

Question 13

What is lost volts?

Answer 13

It is the volts that have been lost to the internal resistance of a battery

Question 14

What is the difference between the terminal pd and the emf?

Answer 14

The terminal pd is the potential difference across the battery.
Terminal Pd = EMF - Lost volts

Question 15

What is the equation for EMF?

Answer 15

EMF = Terminal pd + Lost volts

Question 16

What is the equation for lost volts?

Answer 16

Lost volts = Ir
EMF = V + Lost volts
EMF = V + Ir
EMF = I(R+r) 
Where I is the current, R is the resistance of the circuit and r is the internal resistance

Question 17

What can be obtained from a graph of voltage against current of a battery?

Answer 17

The y axis (voltage axis) intercept is the EMF of the battery.
The Gradient is the internal resistance

Question 18

What is the benefit of having a low internal resistance?

Answer 18

It allows batteries to charge and discharge quicker with more current because they don’t heat up as much.

Question 19

What is a potential divider?

Answer 19

It divides up the voltage so that any value of voltage can be acquired up to the voltage of the supplied power source

Question 20

What does the circuit for a potential divider look like?

Answer 20

12v -----
           [] R1
            |-------- Vout
           [] R2
0v --------------

Question 21

What are the two equations for potential divider circuits?

Answer 21

V1 / V2 = R1 / R2
and
Vout = (R2 / (R1 + R2)) x Vin

Question 22

What is a use of potential divider circuits and how can this be implemented?

Answer 22

They can be used in sensing circuits by replacing one of the resistors with a sensing variable resistor like an LDR or a thermistor

Question 23

What is a potentiometer?

Answer 23

It is a circuit component that changes the value of V out from 0 to Vmax. It works by varying both R1 and R2 at the same time.

Question 24

What is the benefit of a potential divider circuit vs a variable resistor

Answer 24

A variable resistor can only vary the voltage a limited amount where as a potential divider circuit has a larger range that it can vary.