Hello Science People! Today: Go over Reviews 3 and 4 Work on Reviews 5, 6 and 7 Homework: Review Packet

Electric and Magnetic Fields Similarities Are force fields Exert forces of attraction and repulsion The field is strongest near the charge or magnet and gets weaker with distance Differences Electric FieldsMagnetic Fields Created around an electric charge Gets stronger with more charge Created around a magnet OR moving electric charges Gets stronger with more magnetic material or by adding loops to the wire or speeding up the electrons

Induction and Conduction Similarities Both related to static electricity Both involve the motion of electrons Differences InductionConduction Does not involve contact between the charged object and the other object Electrons are NOT transferred but are moved around IN the second object (the charges are separated in the second object Requires contact between the charged object and another Electrons are transferred

Positive and Negative Charges Similarities Both refer to charged objects Both can exert forces on other charged or neutral objects Both are created by the transfer of electrons Differences Positive chargesNegative Charges Result from losing electrons Attract negatively charged and neutral objects Repel positively charged objects Result from gaining electrons Attract positively charged and neutral objects Repel negatively charged objects.

Generators and Motors Similarities Both contain magnets and coils of wire Both have spinning parts Both transform one kind of energy into another Both involve the interactions of magnetic and electric fields Both have electric current in them at some point Differences GeneratorsMotors Transform rotational kinetic energy into electrical energy Spinning the coil of wire in the magnetic field creates an electric current in the wire Transform electrical energy into rotational kinetic energy An electric current moving through the coil of wire creates a magnetic field which pushes against the magnetic field of the permanent magnet causing the motor to spin

Conductors and Insulators Similarities Both are related to the movement of electric charge Both are types of matter Differences ConductorsInsulators Cannot become electrified (they can’t build up a static charge) Tend to be metals Electrons flow through them easily Have lots of outer electrons that move from atom to atom easily Can become electrified (they CAN build up a static charge) Tend to be non-metallic The resist the flow of electrons Electrons are tightly bound to each atom

Permanent Magnets and Electromagnets Similarities Both create magnetic fields Both attract or repel other magnetic materials Differences Permanent MagnetsElectromagnets Created from magnetized material Always creating a magnetic field Strength of the magnetic field depends on the material it is made of Created when electric current flows through a coil of wire Only create a magnetic field when electricity is flowing through them. Strength of the magnetic field depends on the number of loops in the coil and the amount of electric current flowing through it

Charging by Induction

Charging by Conduction

Charging by Rubbing Putting atoms in close contact with each other allows electrons to move from one object to another.

The Law of Electric Charges Like charges repel each other Opposite charges attract each other Uncharged or neutral objects have the same number of positive and negative charges – the charges cancel each other out so there is no extra charge. Charged objects have unequal numbers of positive and negative charges. If it has more electrons than protons, the object has a negative charge If it has more protons than electrons, the object has a positive charge How are charged objects different from uncharged objects?

A negatively charged rod repels a second object. What can you conclude about that second object? Explain! The second object must have a negative charge because it is repelled by the negative rod and like charges repel A negatively charged rod attracts a second object. What can you conclude about that second object? Explain! The second object could have a positive charge because it is attracted to the negative rod and opposite charges attract OR The second object could be neutral and the attraction happens because the negative rod INDUCES a charge in the second object which causes an attraction (this is like the ruler and the pieces of paper example)

Longitudinal vs. Transverse Waves

Sound waves Are mechanical waves (not electromagnetic) Must have a medium (substance) to travel through Space doesn’t have enough matter in it so sound waves don’t have a medium to travel through

Diffraction When a wave encounters some kind of barrier or gap in a barrier and the wave bends around the object