Right Hand Rules # 1 & 2

The right hand rule (or RHR) is a useful little rule for determining the direction of the magnetic field. The Right-hand rule #1 is used for a conventional current to determine the direction of current flow and magnetic field in a conductor. Depending on the information given, you either point your thumb in the direction of the current flow, or coil your fingers so that they point in the direction of the magnetic field. Using the rule, one can figure out which way current flows or which way the magnetic field turns.

 

For example, in the above diagram, if I only knew the current flowed upwards I would point my thumb up and grab the conductor. The direction my fingers coil is the direction the magnetic field is in.

RHR # 2 is used for coils. In a coiled conductor or solenoid, the thumb will always point to the north pole of the magnet and the fingers will point in the direction of current flow. Inside the coil, the thumb also represents the direction of the magnetic field. 

The left hand rules are similar to the right hand rules, except they are used for electron currents, or when the charge flows from negative to positive.

The Tallest Structure

Today in class we had a competition to build the tallest structure using 6 sheets of newspaper and a long strip of tape. My group decided to create a tripod as a base and use the rest of the newspaper to create a long and thin body. While we didn't win, we get some important insights. In order to create a tall structure one must first have a strong base. A solid shape like a triangle is required and it must be somewhat heavy to balance the structure. If a force where to act against one side of the triangle, there would be a leg to support it against the force. For height it's best to have it thin, with it gradually becoming thinner as the structure gets taller so the top won't be too heavy for the bottom to support. The winning group had a structure that was similar to a cone. It was large at the bottom and thin at the top. They used a long strip of paper at the end instead of a rolled up cone to lower the weight.

The center of gravity is the average location of the weight of the object. In a square-based pyramid for example, the center of gravity would be halfway up a line from the center of the square to the tip of the pyramid.

Resistance - Ohm's Law

In any electric circuit, the amount of current that can flow depends on the potential difference of the power supply and the nature of the path connecting the loads and power supply. The more difficult the path, the harder it is for electrons to flow through. The measure of the opposition to the flow is known as resistance.

The formula for resistance is R = V / I , in which R is the resistance is in volts / ampere or ohms (Ω), V is the potential difference in volts (V), and I is the current in amperes (A).


This formula was developed by Georg Simon Ohm and the ratio V / I is known as Ohm's Law. Resistance is determined by several factors such as its thickness, length, cross-sectional area, the material, and it's temperature. The measure for the resistance of a substance is it;s resistivity. The gauge number of a wire refers to it's cross-sectional area. The larger the cross-sectional area, the smaller the gauge number. 


There are two simple ways to connect conductors and loads. The first one is a series circuit, where the loads are connected one after another in a single path. The second is a parallel circuit, where the loads are side by side. 

In a series circuit, the total current is equal to the current of each junction point. The total voltage is equal to the sum of all the potential losses and the total resistance is equal to the sum of all the resistors.


In a parallel, Vt=V1=V2=V3, It=I1+I2+I3, and Rt=1 / R1 + 1 / R2 + 1 - R3

Voltage, Current, and More

In class today we filled in a table that summarized a concept we're already familiarized current, and introduced three new ones: voltage, resistance and watt. It is as follows..

The Energy Ball

In class today we split into groups and received a small ping pong ball with two metal bands on the sides and twelve questions to answer. Through this activity we learned about series and parallel circuits. A series circuit is a circuit in which the loads are connected one after another in series. A parallel circuit is where the loads are connected parallel to each other.

1. Can you make the energy ball work? What do you think makes the ball flash and hum?
Well we managed to make the ball work by touching both bands with our fingers. I believe the ball flashes and hums because of the battery inside.

2. Why do you think you have to touch both metal contacts to make the ball work?
I think that by touching both metal contacts, my fingers act like wires and complete a circuit. This allows the electrons to flow and power the load.

3. Will the ball light up if you connect the contact with any material?
While the ball won't work with any material, it does with anything that is a good conductor of electricity. We managed to make it flash and hum by touching a metal contact with the steel part of a pen and touching the other metal contact with a finger holding the pen.

4. Which materials will make the energy ball work?
Like I stated above, good conductors such as copper and aluminum will make the energy ball work.

5. This ball does not work on certain individuals. What could cause this to happen?
The energy ball might not work for seniors because they lack water in the bodies. Due to their lack of water, they are missing metal in their body and don't conduct electricity as well. Thus the electrons won't flow through their bodies as well and the current won't be strong enough to power the ball.

6. Can you make the energy ball work with all the people in your group?
Yes, we could. By touching fingers and making a chain of people, we just allowed the electrons to flow through a bigger circuit.

7. What kind of circuit can you form with one energy ball?
We formed a series circuit, because the load is connect along a single path.

8.Given two balls can you create a circuit where both balls light up?
Yes we could. By inserting the second ball between two people we made a series circuit with two loads instead of one.

9. What do you think will happen if one person lets go and why?
If one person lets go then both balls will stop humming and the lights will dim. This is because the circuit is broken and the electrons stopped flowing.

10. Does it matter who lets go?
It doesn't matter who lets go because they were still part of the circuit.

11. Can you create a circuit where only one ball lights?
Yes we can. In a parallel circuit with each ball on opposite ends, we can break the circuit of one ball but the other will still be connected to a complete series circuit.

12. What is the minimum number of people required to complete this?
A minimum of four people is required to complete this parallel circuit. 

Current Electricity

Current Electricity is the continuous flow of electrons. In an electric current, energized electrons flow the negative side of a power supply through a complete path or circuit to the positive side of a power supply while directed by a conductor. The model of positive charge flow is known as a conventional current. A load ( any device that uses energy) can be attached to the circuit to be powered.

To find the current in an electric circuit we must first find the total amount of charge that passes a certain point in the conductor and divide it by the time taken. The equation for this is I = Q / t where I represents the current in amperes (A), Q represents the charge in coulombs (C), and t represents the time in seconds. One ampere is the equivalent of one coulomb of charge passing a certain point in a conductor every second. A device which measures current or Ammeter can also be attached to the circuit in order to find the current.

Eg. How much current flows through a washing machine if 2500 c of charge passes through it in 500 s?
      I = Q / t
      I = 2500 c / 500 s
      I = 5 c / s

Thus 5 A of current flows through the washing machine.

There are two types of currents. DC or direct current and Ac or alternating current. In a direct current , the electrons flows in single direction from the power supply through the conductor to a load and back to the power supply again. In an alternating current the electrons will periodically reverse directions.