Electronics Midterm #1

Question 1

Scientific Method

Answer 1

• Observation  Hypothesis  Experiment  Analysis  Conclusion  Communicate Results

Question 2

What is the goal of scientific research?

Answer 2

• Discover laws, suggest theories, and build models that can explain phenomena

Question 3

Describe the differences and similarities between scientific law, scientific theory, and scientific model.

Answer 3

o Laws: describe specific relationships in a concise and quantitative manner
o Theories: explain broader phenomena
o Models: provide simplified representations or complex systems/processes

Question 4

Conservation of energy

Answer 4

• Energy can neither be created nor destroyed

Question 5

Energy:

Answer 5

• Transform (moves within the system) or transfer (energy enters or leaves the system)
• Several types of energy in a system and they can be transformed back and forth without loss

Question 6

• Readily available energy

Answer 6

Kinetic

Question 7

Stored energy

Answer 7

U Potential

Question 8

Hard to recover energy

Answer 8

Eth (thermal energy)

Question 9

Total Energy

Answer 9

Kinetic + Potential + Thermal

Question 10

Energy

Answer 10

ability to do work, change position, temperature, etc.

Question 11

System

Answer 11

• Portion of the physical universe chosen for analysis. Everything outside is called the environment
• E.g. pendulum, electrical circuit w/ battery, wires etc.
• Think about energy and how quickly it can be released (TNT vs. cookie)

Question 12

Forms of energy

Answer 12

• Kinetic: energy associated with motion (equivalent to cash- liquid-readily available)
• Thermal: energy associated with molecular vibrations (internal motion)
• Potential Energy: energy that is stored, must be transformed (equivalent to stocks/bonds)

Question 13

Potential Energies

Answer 13

Gravitational potential energy – height, the higher the more of this
o Elastic potential energy – springs, rubber bands…
o Chemical potential energy
o Nuclear potential energy

Question 14

What is work?

Answer 14

• Positive Work (add energy)
• Negative work (take away energy)
• Work is an energy transfer, then there is at least the implication of force
  o Work = force x displacement
• Work-Energy Theorem: the net work done on a system or by a system is equal to the change in energy of the system
• Energy must go somewhere and come from somewhere
• Law of Thermodynamics: Energy is neither created nor destroyed

Question 15

Power

Answer 15

• Power is the rate of doing work/using energy
• Measured in Watts (W)
• In electric circuits, power is given by the product of the voltage time the current

Question 16

Potential Energy (continued)

Answer 16

• Things move towards lower potential energy
• What determines GPE: mass, height, strength of gravity, etc.
• What causes potential energy?
  o Forces/fields
  o Electric fields can be either attractive (+) or repulsive (-) (gravitational fields only attract)

Question 17

Total Mechanical Energy

Answer 17

KE + GPE + EPE
KE + GPE + EPE (initial) + work external = KE + GPE + EPE (final)
- Remains the same initial = external IF no work external is added

Question 18

What is an electric circuit?

Answer 18

• Closed loop or pathway that allows electric current to flow

Question 19

Energy in the circuit

Answer 19

• As charges move through a battery they move from lower PE (electric PE) to a higher EPE
• As charges move through an electric circuit they move from higher EPE to lower EPE
• Battery stores CPE  EPE  bulb: thermal energy  light energy
• KE of the electric charges does not change as they move through the circuit

Question 20

Big Three

Answer 20

1. Voltage (V) – difference in energy per charge in a circuit, measured in volts (V)
2. Electric current (I) – the rate at which charges move through a circuit, measured in Amps (A)
3. Electric Resistance (R) – a measure of how difficult it is for electrons (charges) to move through a particular part of an electric circuit

Question 21

Ohm’s Law

Answer 21

• V = I R
• -*I is dependent on V and inverse with R
• Ohmic means R is consistent, R = 1/slope, linear

Question 22

Power Law

Answer 22

P = VI

Question 23

Loop Rule

Answer 23

Think about it like an elevator (go up an amount have to go down that amount)

Question 24

3 resistors in series

Answer 24

• 1 loop
• Sharing voltage
• One resistor breaks everything stops
• Current is the same everywhere
• Loop rule: Think about it like an elevator (go up an amount have to go down that amount)
• Battery supplies power, resistors use power
  o Power used by resistors = power from battery
• Total equivalent resistance = sum of resistors resistance

Question 25

- 3 resistors in parallel = 3 loops

Answer 25

- Voltage for battery and resistors is the same - Battery current = sum of resistors current - Junction rule = what enters the junction must leave the junction - Total equivalent resistance = sum of resistors resistance = V/I