04 - Electrical Circuits

Question 1

What do circuits allow us to do?

Answer 1

Manipulate voltages and currents so that we can do what we want (e.g. amplify, attenuate, filter, oscillate…)

Question 2

Name 3 possible circuit components

Answer 2

Resistors
Capacitors
Inductors
Battery (or other DC voltage source)
AC Source (current or voltage)
Ground
Diode

Question 3

In a series circuit, is the overall resistance the sum or product of the individual resistors?

Answer 3

Sum (R1 + R2 = Reff)

Question 4

Which type of circuit is known as a “voltage divider”?

Answer 4

Series circuit

Question 5

In a series circuit, what is the formula to find the current?

Answer 5

I = V/Reff

where Reff = the overall resistance

Question 6

In a series circuit, what is the formula to find the voltage across R1?

Answer 6

R1 (kilo-ohms) x I (mA) = V (volts)

Question 7

In a series circuit, the larger the resistance value, the _____ (lesser/greater) the voltage drop across it

Answer 7

Greater

Question 8

If we know the voltage drops across the resistors of a series circuit, how do we find the voltage of the source?

Answer 8

Voltage of the source is equal to the sum of the voltage drop across the resistors

Question 9

What type of circuit is known as a “current divider”?

Answer 9

Parallel circuit

Question 10

True or False: Just like with water, in a parallel circuit more current flows through the path of least resistance

Answer 10

True

Question 11

What is another name for a variable resistor?

Answer 11

A potentiometer

E.g. Volume dial on Walkman

Question 12

Potentiometers are frequency-_______ (dependent/independent)

Answer 12

Independent

Question 13

Electrical circuits containing only resistors will behave ______ (similarly/differently) for D.C. and A.C signals

Answer 13

Similarly

Question 14

Electrical circuits containing resistors, capacitors, and inductors will behave ______ (similarly/differently) for D.C. and A.C signals

Answer 14

Differently - the electrical characteristics of capacitors and inductors are dependent on the frequency of the A.C. signal (a property which is exploited to design filters and oscillators)

Question 15

With AC, low frequencies give capacitors time to store charge, so the capacitor acts as a(n) _______ (open/short) circuit

Answer 15

Open - flow of electricity will reduce as charge reaches capacitance

Question 16

With AC, high frequencies don’t allow the capacitor time to store charge, so the capacitor acts as a(n) _______ (open/short) circuit

Answer 16

Short - constant flow of electrons back and forth make the capacitor appear as just a piece of conducting wire

Question 17

In a series circuit with headphones, a capacitor acts as a simple ______ (low/high) pass filter, from the perspective of the headphones

Answer 17

High - the high frequencies change rapidly, so the capacitor doesn’t have time to charge, allowing the continued flow of current (low resistance), so there is increased current to, for example, the headphones.
-the low frequencies would allow the capacitor to charge, which would lead to decreased current, so the capacitor would act as an open circuit, blocking the current from reaching the headphones

Question 18

Name one example of a passive element of a typical electrical circuit, and explain why

Answer 18

Resistors
Capacitors
Inductors

The most you can get is the input signal itself

Question 19

Name one example of an active element in a typical electrical circuit and explain why

Answer 19

Amplifiers

They allow your output to be greater than your input signal

Question 20

What are the 3 important classes of electronic circuits?

Answer 20

Attenuators - reduce the input voltage or current, and are typically made of resistive circuits

Filters - attenuate certain frequencies in the input signal

Amplifiers - increase the voltage, current, or power of the input signal while preserving its frequency characteristics. They employ active devices, such as transistors

Question 21

When placed in a parallel circuit with headphones, a capacitor acts as a simple ____ (low/high) pass filter, from the perspective of the headphones

Answer 21

Low - Lower frequencies allow the capacitor to charge, which slows the flow of electrons (more resistance), so the current goes through the alternate pathway (e.g. headphones).
- the higher frequencies don’t allow the capacitor time to charge, so the pressure differential is maintained, and there is low resistance, so the capacitor would get most of the current (as opposed to the headphones).