SciOly Circuit Lab Notes, Study notes of Electronics

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Science Olympiad

By: Urjith Mishra

Table of Contents

• Basics of Electricity……………………………………………………………………………….
• DC Circuit Theory…………………………………………………………………………………
• What is Current?……………………………………………………………………………….....
• What is Voltage?.................................................................................................................
• What is Resistance?...........................................................................................................
• Ohm’s Law………………………………………………………………………………………...
• Relationship to Water…………………………………………………………………………….
• Coulomb’s Law……………………………………………………………………………………
• Right-Hand Rule……………………………………………………………………………….....
• Kirchhoff’s Voltage Law………………………………………………………………………….
• Kirchhoff’s Current Law………………………………………………………………………….
• Analyzing Circuits With Kirchhoff’s Laws………………………………...……………………
• Magnets………………………………………………………………………………………..…
• Transformers and Motors……………………………………………………………………....
• Transformers…………………………………………………………………………………….
• Motors…………………………………………………………………………………………….
• Diodes…………………………………………………………………………………………….
• Standard Diodes………………………………………………………………………………...
• Light Emitting Diodes.…………………………………………………………………………..
• 3-Way Switches………………………………………………………………………………….
• Static Electricity………………………………………………………………………………….
• Popular Circuits………………………………………………………………………………….
• Famous Scientists……………………………………………………………………...….…....
• Nikola Tesla……………………………………………………………………………...……....
• Alessandro Volta………………………………………………………………………………...
• Heinrich Hertz…………………………………………………………………………………....
• Georg Simon Ohm…………………………………………………………………………..…..
• Michael Faraday…………………………………………………………………………………
• André-Marie Ampère…………………………………………………...……………………….
• Charles-Augustin de Coulomb…………………………………………………………………
• Gustav Robert Kirchhoff……………………………………………………………………......
• Resistor Color Code…………………………………………………………………………….

DC Circuit Theory

What is Current?

● Current is the rate of flow of charge past a particular point or region. ● In circuits, an electrical charge is normally carried by electrons. ● In electrical conductors, the atoms are bonded in a way where the electrons are able to move around the material without sticking to a particular atom. ● This allows the electrons to "flow." ● the movement of individual electrons within a conductor, known as the electron's drift velocity is quite slow (around several micrometers/second for 1 A in a 2mm diameter copper wire.) ● Current is like the flow in water. ● Current is measured in amperes. ● Amperes are also known as amps. ● High current can heat things up. ● Negative(-) to Positive(+) is known as electron flow. ● Positive(+) to Negative(-) is known as conventional flow. Direct Current ● Direct current has constant direction. ● All batteries have direct current. ● Direct current is also known as DC. ● Most electronics use direct current. ● DC currents are much less hazardous than AC currents. But, if you get in contact with a wet surface, and then touch a DC current, it can be very hazardous. Alternating Current ● Alternating current regularly reverses direction. ● An alternating current is also known as AC. ● Alternating current is more dangerous than direct current. ● Alternating current has less power loss to heat during transmission. ● Alternating current is used for generation and transmission. ● House electricity and power lines use alternating current. ● Alternating Current is transmitted at very high voltages and stepped down using a transformer for home usage (normally around 220V AC in the US).

What is Voltage?

● Voltage is the force behind electrons. ● Batteries range from 1.5 volts to 24 volts. ● Home electricity ranges from 110 volts to 220 volts. ● Lightning can be millions of volts. ● Voltage is also known as a potential difference. ● Voltage is similar to pressure in water. ● Voltage is measured in volts. ● The symbol/abbreviation for a volt is V.

What is Resistance?

● Resistance is the opposition against the free transfer of electrons in a conductor. ● Copper, Silver, and other conductors have low resistance. ● Glass, wood, rubber, plastic, and other insulators have high resistance. ● Transfer (or current) is usually due to some force like the EMF(Electromotive Force) from the voltage of a battery. ● The wider the wire is the less resistance it has. ● Resistance is like how difficult it is for water to flow. ● Resistance is measured in ohms(Ω). ● Always have tables of resistivity, ρ units are Ω•m ● Superconductors = 0 Ω•m ● Metals/Conductors ~10-8 Ω•m ● Semiconductors (variable upon doping) ● Insulators ~1016 Ω•m ● Superinsulators ~∞ Ω•m ● Top Common Conductors ● Silver ρ = 1.59x10-8 Ω•m ● Copper ρ = 1.68x10-8 Ω•m ● Gold ρ = 2.44x10-8 Ω•m ● Aluminum ρ = 2.65x10-8 Ω•m ● Top Common Semiconductors ● GaAs ρ = 1x10-3 to 1x108Ω•m ● Germanium ρ = 4.6x10-1Ω•m ● Silicon ρ = 6.4x102 Ω•m ● Top Common Insulators ● Deionized water, Glass, Diamond, Hard Rubber, Air, and Dry Wood ● Fused Quartz ρ = 7.5x1017Ω•m ● PET ρ = 1x1021Ω•m ● Teflon ρ = 1x1023 to 1x1025Ω•m

Right-Hand Rule

The current enters from the arm and is induced to go right. The force is motion, like a motor, and the magnetic field is a magnetic field.

Kirchhoff’s Voltage Law

The sum of all voltages must be equal to 0.

Kirchhoff’s Current Law

The current entering any junction is equal to the current leaving that junction. i2 + i3 = i1 + i4. A charge is conserved. Therefore, the current that flows into a resistor equals the current that flows out of the resistor. Similarly, the current that flows into a junction must equal the sum of the currents leaving the junction.

Step 4: Calculate the “drop” and repeat from step 3 until you reach where you started. You should have a value of 0. Step 5: Drop can also be a negative rise. Step 6: Double-check your work with the equation below.

Magnets

Electromagnets

Magnetism - the force exerted by magnets What causes magnetism: There are 2 main ways that magnetism can arise: Moving Charges / Electron magnetic moments and electric current: -Electric current: The movement of electric charges creates a magnetic field surrounding the moving current because of the following

1. Electron’s property of spin (which are electron magnetic dipole moments)
2. And, The electron’s motion around the proton that’s known as the electromagnetic field. -Electron magnetic dipole moment: This occurs when an electron has a magnetic moment (or creates magnetism) because of its intrinsic property of spin. Yet, this normally cancels out with other electrons, but sometimes-either spontaneously, or owing to an applied external magnetic field, each of the electron’s magnetic moments can be added together and produce a net total magnetic field. Nuclear magnetic moment (of atomic nuclei): Because of how these moments are thousands of times smaller than electrons magnetic moments, they are negligible in the magnetization of materials. Electric field flows from positive to negative. Magnets : ● Magnets always have 2 poles and are considered to be dipoles. ● They will always be magnetic fields. ● Always comes in the form of dipoles. ● Theoretically, a magnetic monopole is possible but has never physically worked. ● If a dipole magnet were cut in half it would have 2 dipole magnets. ● Electrostatic forces and magnetic forces are the same thing. Yet, they are typically treated as 2 different things. ● Poles will always find the shortest path. ● Magnetic poles always flow from North to South

If you break a permanent magnet into 2, you will have 2 magnets. Geomagnetism/ Earth’s magnetic field: The Earth is surrounded by an immensely large magnetic field called the magnetosphere.

Geomagnetism Definitions:

Solar Winds : A stream of charged particles from the sun. Van Allen Belts : Magnetic region above Earth; in the atmosphere. Magnetic Declination : Angle between geographic north/south and magnetic north/south. Compasses - A device that shows where one is based off how the magnetic needle points north. Different Magnets Ferromagnets - magnetize readily Paramagnets - slightly magnetic Diamagnets - do not magnetize readily Ferromagnetism definition : A Mechanism by which certain materials form magnetic domains. Paramagnets : Magnets that are attracted to externally applied magnetic fields. Not permanent magnets. Repelled by magnetic fields Diamagnets : Magnetic materials that are repelled to an externally applied magnetic field. Not permanent magnets. Repelled by magnetic fields Diamagnetism : When an applied magnetic field creates an induced magnetic field within the Diamagnetic materials in the opposite direction, causing a repulsive force. Paramagnetism : When an applied magnetic field creates an induced magnetic field within the paramagnetic and ferromagnetic materials in the same direction causing them to be attracted by the magnetic field. Magnetic flux density - The amount of how compact the magnetic field is. Units - Tesla or Gauss (not gausses). The Earth’s ‘north’ pole is actually a south pole! This is why the north side of the compass needle points north. Electromagnets : Are temporary magnets, operated by electric current, and can change their magnetic

field strength/ magnetic flux density (they both show increases in magnetic field intensity). Due to how current has the property of magnetism; when current is passed through a solenoid, it is able to induce a polarized magnetic field. These are used for generators and motors because of how they can induce polarized magnetic fields (and thus a force as according to Fleming’s right hand rule) and EMF. How to make an electromagnet stronger:

1. Increase the amount of coils in solenoid.
2. Greater diameter of ferromagnetic core (typically iron)
3. The increase voltage traveling through circuit/ electromagnet Solenoid : A cylindrical coil of wire acting as a magnet when carrying electric current. Fleming's Left and Right Hand Rule Fleming’s Right Hand Rule : Fleming’s Right hand rule is a hand sign that is used for figuring out which direction the current is flowing towards within an electric generator. Note: Fleming’s Right Hand Rule can only be used when you are using electric generators. Fleming’s Left Hand Rule : Fleming’s Left Hand Rule is a hand sign that is used for figuring out which direction the current is flowing towards within an electric motor. Note: Fleming’s Left hand Rule can only be used when you are using electric motors. Magnetic Monopoles - magnets that only have 1 pole Gauss’s Law of Magnetism In physics, Gauss's law for magnetism is one of the four Maxwell's equations that underlie classical electrodynamics. It states that the magnetic field B has divergence equal to zero, in other words, that it is a solenoidal vector field. It is equivalent to the statement that magnetic monopoles do not exist. Rather than "magnetic charges", the basic entity for magnetism is the magnetic dipole. (If monopoles were ever found, the law would have to be modified, as elaborated below.)

Motors

● Can be brushed or brushless. ● It has an electromagnet repel against another magnet. ● Uses the right hand rule. ● Coils are used as electromagnets. ● Brushed motors use brushes to change contact in the commutator ring. ● Brushless motors are used for heavy duty tasks because brushes can wear out. ● Universal motors use 2 electromagnets on the same power source. ● Motors can be used as generators in reverse. Brushed Motor Diagram Brushless Motor Diagram

Diodes

Standard Diodes

● Two types of doping, N, and P. ● It only allows current one way. ● Doping is added to a semiconductor such as silicon. ● N-doping has added electrons that try to run away. ● P-doping has slots for electrons that cause electrons to go in empty slots. ● The border between the N and P doping is slightly positively charged with another border slightly negatively charged. This border is called ‘the depletion region. ● The depletion region will only allow flow 1 way when connected to the charge.

Light Emitting Diodes

● Three important factors are the polarity, forward voltage, and max current. ● There is an anode and cathode these are the 2 leads. ● Light is created by positive charges colliding with negative charges. ● Longer side is anode and the shorter side is cathode. ● If you exceed max current then the LED can burn. ● Some approximate ratings are below.

Static Electricity

Static Energy :

This is electricity that doesn’t flow. It has a voltage but no current. Caused by

over/underpopulated electrons in an object. We learned that atoms are made up of tiny

particles called neutrons, protons, and electrons. The neutrons and protons make up the

nucleus. The electrons spin around the outside of the nucleus. A static charge is formed

when two surfaces touch each other and the electrons move from one object to

another. One object will have a positive charge and the other a negative charge. Rubbing

the items quickly, like when you rub a balloon fast over something or your feet on the

carpet, will build up a large charge. Items with different charges (positive and negative)

will attract, while items with similar charges (positive and positive) will push away from

each other. Sort of like a magnet. One example of this is when you slide down a slide

and all of your hair stands up straight. This is because the friction of sliding has caused

a positive charge to be built up on each hair. Since each hair has the same charge, they

all try to push away from each other and end up standing up straight.

Dangers of Static :

• Static electricity builds up in clouds which cause a huge spark to form between

the ground and the cloud. This is called lightning - a flow of charge through the

atmosphere.

• It is dangerous when there are flammable gases or a high concentration of

oxygen. A spark could ignite the gases and cause an explosion

• Touching an object with a large electric charge will allow the charge to flow

through your body, causing an electric shock. This could cause burns and heart

stoppage.

• Refuelling aircrafts/tanker can be dangerous. When fuel passes through the

hose, this could build up static charge, cause a spark, and ignite the fuel.

Popular Circuits

Wheatstone Bridge