Blog 6: 10 points from pages 582 ~ 589

1.         Magnetic field: the distribution of a magnetic force in the region of a magnet à 2 different magnetic characteristics, labelled north and south ß responsible for magnetic forces.

2.         North + North and South + South, repel each other
North + South, attract each other.

3.         Magnets also attract certain metals, such as iron, nickel and cobalt ß these are called ferromagnetic metals.

4.         Domain Theory: All large magnets are made up of many smaller and rotatable magnets ß dipoles. Dipoles can interact with other ones close by. If the dipoles line up, then a small magnetic domain is produced.

5.         Oersted’s principle: charge moving through a conductor produces a circular magnetic field around the conductor.

6.         Mapping the magnetic field allows you to predict the direction of the electromagnetic force from the current.

7.         Right-hand rule allow you to take certain known factors and predict one unknown factor. There are three right-hand rules.

8.         Right-hand rule #1 (RHR#1) for conventional current flow: grasp the conductor with the thumb of the right hand pointing in the direction of conventional, or positive (+), current flow. The curved fingers point in the direction of the magnetic field around the conductor.

9.         Rule #1 allows you to turn the magnet on and off ß current flow through the conductor is interrupted. 

10.     Rule #2: coiling the wire in a linear cylinder straightens out the field

11.     Right-hand rule #2 (RHR#2) for conventional current flow: grasp the coiled conductor with the right hand such that curved finger point in the direction of conventional, or positive (+), current flow. The thumb points in the directs of the magnetic field within the coil. Outside the coil, the thumb represents the north (N) end of the electromagnet produced by the coil.

 

12.   Formula comparison of strength of magnetic fields (B).

Current in the coil:
B₁=B₂(I₂/I₁)

Number of turns in the coil:
B₁=B₂(n₂/n₁)

Blog 5: 10 points from pages 553-563

1.       The amount of current flow in a circuit, and therefore the amount of energy transferred to any useful device depends on two things:

  I) The potential different of the power supply (the amount of push).

  II) The nature of the pathway through the loads that are using the electric potential energy.

2.       Resistance = the measure of opposition to current flow.

3.       R = V / I
R = Resistance in volts/ampere
V = Potential Difference in volts (V)
I = Current in ampere (A)

4.       This is called Ohm’s law (R = V / I)

5.       The amount of current flowing through a resistor varies directly as the amount of potential difference applied across the resistor as long as other variables, such as temperature, are controlled.

6.       Thinner wire has a larger resistance than a thicker one

7.       Properties of conductors that affect the resistance:
I) length (The longer the conductor, the greater the resistance e.g. if length is doubled, resistance is doubled)
II) cross-sectional area (The larger the cross-sectional area or thickness of the conductor, the less resistant it has to charge flow e.g. if cross-sectional area is doubled, the resistance becomes half)
III) type of material (some material are better conductors e.g. if resistivity, the general measure of the resistance of a substance, is doubled, the resistance is also doubled)
IV) temperature (greater molecular motion during high temperatures increase the resistance)

8.       The gauge number of a wire indicates its cross-sectional area (small gauge number has a large cross-sectional area)

9.       Superconductivity = the ability of a material to conduct electricity without heat loss due to electrical resistance.

Kirchhoff’s Law

1.       Kirchhoff’s current law – The total amount of current into a junction point of a circuit equals the current that flows out of the same junction.

2.       Kirchhoff’s voltage law – The total of all electrical potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop.

3.       In any circuit, there is no net gain or loss of electric charge or energy.

4.       Resistance in Series à R_T = R₁ + R₂ + R₃ + … + R_N
N = the total number of series resistors in the circuit

5.       Resistance in Parallel à

Blog 4: Prelab Chart

Blog 3: Energy Ball Experiment

What is the difference between a parallel and series circuit?

A parallel circuit can turn one bulb or other kinds of materials off while the other bulb connected to the same circuit can still be working. A series circuit cannot do that.

                                    Parallel circuit                               Series circuit

1. Can you make the energy ball work? What do you think makes the ball flash and hum?

Yes, I can make the energy ball work, by touching the metallic parts of the energy ball with both my hands. Electricity is what makes the ball flash and hum.

2. Why do you have to touch both metal contacts to make the ball work?

The fingers act like a conductor that connects the circuit within the energy ball together.

3. Will the ball light up if you connect the contacts with any material?

No, only materials that conduct electricity will work.

4. Which materials will make the energy ball work? Test your hypothesis.

Anything that is a good conductor of electricity will work (e.g. metal)

5. This ball does not work on certain individual - what could cause this to happen?

This would happen if a person touches the metallic parts with interference of insulation materials in between (for example, a person wearing rubber gloves)

6. Can you make the energy ball work with 5-6 individuals in your group? Will it work with the entire class?

Yes, it will work as long as the individuals are in contact with each other.

7. What kind of a circuit can you form with one energy ball?

Series circuit

8. Given two balls (combine two groups): can you create a circuit where both balls light up?

Yes, by forming a circle with the energy ball held by different individuals.

9. What do you think will happen if one person lets go of the other person’s hand and why?

I think that if one person lets go of the other person’s hand, both of the energy ball will stop working because the circuit will not be complete.

10. Does it matter who lets go? Try it.

In a parallel circuit, if a person from one side of the circle lets go, the energy ball on that side will stop working while the energy ball on the other side will still work. In a series circuit, it does not matter who lets go, the result is the same.

11. Can you create a circuit where only one ball lights (both balls must be included in the circuit)?

Yes, in a parallel circuit, with one circle connected and the other unconnected.

12. What is the minimum number of people required to complete this?

It takes the minimum of 3 people to complete a parallel circuit.

Blog 2: Challenge on September 8, 2010

What are the physics of tall structures?

The physics of tall structure are the balance of the structure (how well-balance it is) and the weight of the structure (gravity). In order for a structure to balance well, it has to find its centre of gravity. The weight also plays an important role since the amount of weight is what makes a structure balance.



What makes a tall structure stable?

A strong, firm base is really important since it carries the weight of the whole structure. The top of the structure cannot be too heavy. The supporters must also be firm. The shape and sides of the structure must be well-balanced.



What is the centre of gravity?

The centre of gravity is when the weight of the opposite side is equal to the original side. If the centre of gravity is found, it will allow the structure to be well-balanced.

Blog 1: 10 points from page 544-552

1. Electric current involves electrons repelling one another and passing through a conductor. Energized electrons, directed by a conductor, allow energy to be used to power many devices.


2. Electric current: the flow of charge.

3. Current (I): the rate of charge flow.

4. Formula for current is:

                                        I: Current in amperes (A)

                                        Q: Charge in coulombs (C)

                                         t: time in seconds

5. Conventional current is current flow from positive to negative while Benjamin’s theory was that it was from negative to positive

6. Ammeter: a device that measures current

7. Direct current (DC): current that flows from power supply through the conductor to a load in a single direction. Alternative current (AC): current that changes directions periodically.

8. Circuit: the path of current and is mandatory for an electrical device.

9. Electric potential difference (V): electrical potential energy for each coulomb of charge in a circuit. Also known as voltage. Formula for potential difference is:

                                                                 V=E/Q

                                               V: Voltage/potential difference

                                                               E: Energy

                                                               Q: Charge

10. Coulomb = a group of electrons

11. Formula for energy in joules is:

                                                        E=VIt

                                                E: energy in joules

                                       V: potential difference in volts

                                              I: current in amperes

                                               t: time in seconds

12. Voltmeter: a device that measures potential different between two points.

13. electrical energy always originates from some other form of energy (chemical, mechanical, thermal, or light energy)