Static charge/electric force
An object has an equal amount of protons and electrons, what charge is it?
Neutral. 0 charge
What is the formula for Ohm's Law?
V = I R
The 4 things a circuit needs:
1. Source
2. Conducting wires
3. switch
4. Load
A current of 0.5 A flows through a 22 Ω resistor. What is the value of the voltage across it?
11 V
What are the positive and negative electrodes called?
Cathode and anode
Materials that do not let electrons move through them easily are called
conductors
What is voltage also called?
Electrical Potential Energy
A circuit has an open switch. What happened to the lightbulb in the circuit and why?
The lightbulb turns off because the circuit is disconnected - no electrons are flowing through the wires into the lightbulb.
A current of 300 A flows through a 12 V lamp. What is the resistance of the lamp?
0.04 Ohms
Describe the currents in parallel circuits. (Branches vs main branch)
The sum of the smaller branches' currents will add up to the main branch.
What is a device that can be used to detect the presence of charge?
electroscope
Define current (also symbol and unit)
Current is the rate of movement of electrons through a conductor. (symbol is I, unit is Amperes)
Describe what a series circuit is.
A series circuit has multiple loads but only one pathway for the electrons to flow.
In a conductor, if 6-coulomb charge flows for 2 seconds. The value of electric current will be
3 amperes.
How does an electroscope determine the level of charge on an object?
The gold leafs will separate immediately if a strongly charged object touches the metal conductor. The electrons from the object will flow through the metal into the gold leafs and the leafs will both become negatively charged and repel each other.
A vinyl rod is rubbed with a cotton cloth. The vinyl rod is able to pull small pieces of paper to it. Describe in detail what happened and why.
The vinyl rod because charged by friction and picks up electrons from the cotton cloth, becoming negatively charged. The paper is neutrally charged and charged objects attract neutral objects.
In which of the following cases is Ohm's law not applicable?
a) Electrolytes
b) Vacuums
c)Arc Lamps
D) insulators.
Insulators. The electrons are unable to move freely and current would be greatly inaccurate
In a parallel circuit what is the place where pathways separate and join back together?
junction point
What is the current in the series circuit if:
load 1: 8v and 4 ohms
load 2: 6v and 3 ohms
Current is (8v+6v)/(4+3 ohms) = 14v/7ohms = 2 A
You add up the voltages and resistances because this is a series circuit.
Describe the difference between a wet cell and a dry cell
A wet cell uses liquid electrolytes while a dry cell uses paste as an electrolyte.
When a plastic comb comes close to a running stream of tap water the water starts to bend towards the comb. Then after a while the water stops bending towards the comb. Explain the physics behind what you observe here.
The comb must be charged negatively as it is plastic and likes to keep electrons on its surface. The electrons are attracted to the protons in the water and pulls it towards it. However, after a small period of time the water becomes charged by induction (not touching) and the difference in charge is negligible - making them not longer attracted to each other.
Define resistance (symbol and unit) AND explain how it works.
Works against and slows down the motion of electrons. R and Ohms. How resistance works is dependant on the property of a substance and how it can convert electrical energy into other forms of energy. EG. filaments of a lightbulb convert the energy into light and heat. Less of a conversion = less resistance. More conversion = more resistance.
Describe the similarities and differences between conventional current flow vs electron current
conventional current is from the positive cathode to the negative anode but the electron current describes how electrons are flowing from the negative anode the the positive cathode
There are 3 loads across a series circuit. 1st load has 6v, 2nd load has 4v, and 3rd has 8v. What is the current flowing through each load and the resistances of load 2 and 3 if load 1 has a resistance of 3 Ohms.
I = V/R so 6v/3 ohms = 2 A for load 1. In a series, the current is the same throughout the whole circuit so 2 A is the current for load 2 and 3 as well.
The resistance for load 2 is R = V/I = 4v/2A which is 2 Ohms.
Load 3 is 8v/2A which is 4 ohms.
I placed another lightbulb into the circuit which cause the current to increase on the ammeter. Describe what circuit this must have been and how this increase in current was caused.
It must be a parallel circuit and the lightbulb must have been added to create another pathway. Even thought the lightbulb adds resistance to the circuit, the additional pathway decreased the overall resistance of the circuit. V= IR, so when resistance is decreased, voltage is same (battery), the current increases.