Home » Physics » Electromagnetism » Currents and DC circuits

# Currents and DC circuits

## A battery and a bulb

More examples at Electronics page by V. Ryan. TechnologyStudent.com

## The only way for a bulb to light

The circuit must go through the lightbulb.
Image from Physicsclassroom .com

## Making a schematic diagram of a real circuit

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### Electricity circuits intro

• Look inside simple electrical appliances
• What are circuit diagrams
• 2 types of electrical charges
• what is an electrical current

### Static Electricity, Unit of Charge, Coulombs

• What is static electricity? (and why is this term a misnomer?)
• unit of electric charge is the Coulomb
• How is the Coulomb defined?

### Measuring Electricity. Recharging a battery.

• Direct Current (DC) circuit : the water flow analogy
• how to measure voltage drops
• current is the flow of electrical charges
• batteries don’t really lose charge – they lose energy

### Measuring current. AC power. Resistance

• Measuring current with an ammeter
• households uses AC
• conductors, insulators and semiconductors – their resistance
• V, I and R relationships

### In which direction do charges flow?

• Do + charges move, or do – charges move?
• Do all electrical currents flow in the same direction?
• In ReDox chemical reactions, we can have two different currents, flowing in different directions, at the same time. Let’s see how.

### Ohm’s law and resistors

• Ohm’s “law” is true for many materials
• Yet not all electrical devices obey Ohm’s law
• Potentiometers (variable resistors)

### Electric Power: kilowatt-hour

• Units and symbols for: electrical work, energy and power
• appliances are rated by power (Watts)
• measuring power in a circuit
• measuring electricity by the kilowatt-hour
• calculating the cost to run electrical devices

### Series & Parallel Circuits. Safety. Circuit breakers. Kirchhoff’s laws.

• Series circuits and parallel circuits
• circuit breakers or fuse-boxes as safety devices
• Find voltage drops in a series circuit: conservation of energy
• Kirchhoff’s law: In a circuit, voltage changes must add up to zero
• Open circuits, closed circuits, and short circuits
• Why short circuits are dangerous

## Kirchhoff’s laws

### Animations of Kirchoff’s voltage law:

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## Safety (Circuits and overheating)

### A GFCI on a hair dryer.

Lab Measuring Voltage Current DC circuits

• Learn how to build a simple circuit, measure voltage, and current
• Build a DC series circuit and DC parallel circuit

### Chemical reactions occur within battery. e- are stripped away from the carbon electrode. e- try to flow from – terminal to + terminal, if a conducting circuit exists.

Here’s an amazing explanation: How A Battery Works – John Denker Av8n.com

In Physics forums we find these details.
Contributor leright writes:

Inside the battery, the negative charges flow IN THE DIRECTION OF THE E-FIELD, which means the negative charges are going AGAINST the electrostatic force set up inside the battery.
The electrons are able to flow against the electrostatic force because of an opposing chemical potential.
Normally, a battery which is not shorted out or connected to a load is under equilibrium conditions, meaning the chemical potential inside the battery exactly equals the electrical potential. Under these conditions, no charge carriers flow.
If you connect the positive terminal of the battery to the negative terminal, through some load, the electrons at the negative terminal of the battery flow through the wire to the positive terminal by the electric field set up by the E-field external to the battery.
When these electrons reach the positive terminal, the E-field inside the battery is momentarily reduced which in turn upsets the equilibrium between the chemical and electrical potential.
The chemical potential then dominates and allows the negative charge to continue flowing from positive terminal to negative terminal until equilibrium is once again established.
Notice that the electrons flow AGAINST the coulomb force inside the battery. They are able to do this because of the chemical potential, which is slightly greater than the electrical potential when equilibrium is disturbed.
The whole point is that the flow of electrons (and ions) is not controlled by the electrostatic potential, but by the ELECTROCHEMICAL potential.
That electrochemical potential is also function of the concentrations of chemicals and a battery is exactly such a structure, where the gradient in electrochemical potential and the gradient in electrostatic potential are in opposite directions.
Hence, it is the electrochemical potential which drives electrons and ions against the electrostatic force.
Of course, the electrostatic potential is a PART of the electrochemical potential.
So it is true that the electrostatic force tends to diminish the tendency to flow against the E-field, but if the concentration gradients can overcome this, then nevertheless, the charges flow against the electrostatic force.
The price to pay is that this flow will change the concentrations of chemicals in exactly the way which is necessary to “drop” the gradient of the electrochemical potential.
The system reaches a static condition when the electrochemical potential is equal everywhere: in that case, charges are not “motivated” to move anymore.
This situation can STILL contain both a gradient in electrostatic potential and a gradient in concentrations.

This is BTW, what happens in a PN junction in a semiconductor. There, you DO have an E-field, and NO charges flowing (because they are pushed exactly the same amount in the opposite direction by the concentration gradient, and both cancel).

E-field-inside-of-a-battery: Physics Forums

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### Electric-magnetic fields flow outside wires, like this:

In a simple circuit, where does the energy flow? – William J. Beatty