## Electricity and Magnetism

According to the CSET website, there will be 6 muliple choice questions and no Constructed Response Question.

**a. Describe and provide examples of electrostatic and magnetostatic phenomena**

Electrostatic is a phenomena that comes from the forces that electric charges exert on each other. The force is between two charges. If they are of opposite charges, then they attract each other, and if they are the same charge, then they repel each other. Electrostatic occurs when there is a buildup of charge on a surface of an object. This may be due to contact with other surfaces. The electrostatic force between these charges are very strong and is difficult to separate opposite charges. Examples of electrostatic phenomena include static and electricity produced from a magnet.

Magnetostatic is the study of magnetic fields. Magnetostatic phenomena explains that charges are either stationary or in a direct current.

Magnetostatic is the study of magnetic fields. Magnetostatic phenomena explains that charges are either stationary or in a direct current.

**b. Predict charges or poles based on attraction/repulsion observations**

Objects that are strongly magnetic are called ferromagnetic. They may either be hard (which doesn't lost its magnetism after being magnetized easily; or soft, which does lost its magnetism after being magnetized). When an object is magnetized, all the dipoles (molecular magnets) become aligned. A magnet's pole is a point in a magnet at which it's magnetic force is concentrated. The two poles, north and south pole, point to it's magnetic pole, south or north magnetic pole. The first law of magnetism states that like poles repel and that unlike poles attract.

**c. Build a simple compass and use it to determine direction of magnetic fields, including the Earth’s magnetic field**

A compass uses a lightweight magnet and a low friction pivot that allows the magnetic needle to point to the magnetic north (North Pole).

Materials:

1).Needle

2) Bar magnet

2) Shallow dish with water

3) Floating object such as a cork or bottle cap.

4) optional: marker and masking tape

Process:

Stroke the needed 20-30 times with the end of a bar magnet. This process will magnetized the needle, a process called single touch. Place the magnetized needle on top of the floating object and place the items in a shallow dish of water. Slowly, the needle will move so that it aligns with the magnetic north pole. Using the marker and the masking tape, you can now label the dish with north, south, east, and west.

Materials:

1).Needle

2) Bar magnet

2) Shallow dish with water

3) Floating object such as a cork or bottle cap.

4) optional: marker and masking tape

Process:

Stroke the needed 20-30 times with the end of a bar magnet. This process will magnetized the needle, a process called single touch. Place the magnetized needle on top of the floating object and place the items in a shallow dish of water. Slowly, the needle will move so that it aligns with the magnetic north pole. Using the marker and the masking tape, you can now label the dish with north, south, east, and west.

**d. Relate electric currents to magnetic fields and describe the application of these** **relationships, such as in electromagnets, electric current generators, motors, and** **transformers**

**Electric current**is the rate of flow of electric charge (electrons). In a magnetic force, the force between two moving charges can be electric currents.

**Electromagnetics**have several applications, all of which attract metals when they are switched on. They convert electric energy to mechanical energy.

On the other hand,

**electric current generators**produce electric current from mechanical energy.

**Electric motors**uses the Lorentz force (a current-carrying wire that goes through a magnetic field which can produce movement) to transform electrical energy into mechanical energy.

A

**transformer**consist of two coils of wire that is wound onto the same core of soft ferromagnet (unable to retain its magnetism) material . A transformer is used to change an alternating electromotive force in one of the coils to a different electromotive force in the other coil. It can change the values of voltage and current without changing the frequency. It consists of a primary and secondary coil.

The first coil in a transformer is connected to the AC voltage and is called the

**primary coil**.

The second coil is the one in which an AC voltage is induced and is called the

**secondary coil**.

**Step-up transformer**has a secondary coil that is greater, has more turns, than that in the primary coil. Increases voltage.

**Step-down transformer**has a secondary coil that is less, fewer turns, than that in the primary coil. Reduces voltage.

Turns ratio is the ratio of the number of turns in the secondary coil to the number of turns in the primary coil.

**e. Design and interpret simple series and parallel circuits**

**Simple series circuit:**A simple series circuit is a circuit that involves only one path for the electrons to travel.

A simple circuit consists of three elements: a source of electricity (such as a battery), a path or conductor for electricity (electrons) to flow through (such as a wire), and an electrical resistor (such as a light bulb). The flow of electrons starts from the low potential terminal (negative terminal) of the battery, passes through the light bulb, and back to the high potential (positive terminal) of the battery. Current flows from high potential to low potential.

Christmas lights can be an example of a simple series circuit. If you take a bulb out, then the rest of the lights will not be lit anymore. This is because there is now an open circuit and the current can no longer flow through the circuit.

A flashlight is another example of a simple series circuit, with a switch, light bulb, battery, and wires connected to form a circuit, .

In a

**parallel circuit**, electrons has several paths that it can take. For example, in a parallel circuit, there could be two resisters, such as light bulbs, on two different wire paths. Electrons can choose which path through the resistor to take. The total current is equal to the sum of the currents in the indiviual paths. I= I1 +I2 + I3.... All elements have equal voltage. V= V1 = V2 = V3.... The total resistance decreases as more paths with resistors are added to the circuit. 1/R = 1/R1 + 1/R2 + 1/R3... Total resistance is always less than the smallers individual resistance.

This of a light switch that controls the lights in a hallway at home. If one of those lights goes out, the other still stays lit.

If the electrons move in one direction, then it is called direct current. If the electrons is constantly being revered forwards and backwards, then it is called alternating current.

Volt: unit that measures a battery's strength

**f. Define and calculate power, voltage differences, current, and resistance in simple circuits**

**Power**is the force motivating electrons to flow, called

**voltage**. It is the measurement of potential energy that is relative between two points. Voltage is measured in volts. To solve for the voltage (E), you multiply current (I) times resistance (R).

E=I x R

**Current**is the continuous movement of electrons in a circuit.

**Resistance**is the opposition to motion. Resistors are important otherwise too many electrons will move through the circuit.

Find the total resistance for both a series circuit and parallel circuit:

**Series Circuit:**

**Parallel Circuit:**

To find the total current:

I=E/R

Thus, the total current (I) is found by taking the voltage of the power source and dividing it by the total resistance.

I=E/R

Thus, the total current (I) is found by taking the voltage of the power source and dividing it by the total resistance.

Using the illustration above, we can find the total current using Ohm's Law:

I= 12 V/3 ohm

I = 4 Amps

Find the total current if the voltage is 5 and the total resistance is 12.

I= V/R

=5/12

= .42 Amps

© Science CSET: Free Prep Guides, 2008. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Science CSET: Free Prep Guides with appropriate and specific direction to the original content.

I= 12 V/3 ohm

I = 4 Amps

Find the total current if the voltage is 5 and the total resistance is 12.

I= V/R

=5/12

= .42 Amps

© Science CSET: Free Prep Guides, 2008. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Science CSET: Free Prep Guides with appropriate and specific direction to the original content.