Unit 3 - Chemistry Flashcards
Explain why two objects made of different materials can obtain a charge when they are rubbed together.
Since the materials are different they have different pulls towards electrons. Meaning, that one material will pull electrons off of the other when they when they are separated after being rubbed. Resulting in both of them becoming charged. If they were the same material, none of them will have a stronger pull than the other. So, none of them will gain or lose electrons.
Which are better for holding static electric charges: insulators or conductors? Explain why.
Insulators are better because they hold electrons tightly, so they cannot move around freely. The charge only stays in the spot where rubbed.
What are lightning rods, and how do they offer protection to tall buildings?
A lightning rod is usually made of metal. There is also a wire that goes from the rod into the ground. It provides a safe path for lightning to follow to the ground.
State 4 factors which affect the resistance in a wire
Temperature - When the metal wire is heated , more energy is given to the atoms,
therefore they vibrate more. From this there is a greater chance of
collisions with the electrons and they are impeded more, therefore
less charge is passed by the electrons and the resulting current is
reduced.
Length of wire - if the length of a wire is increased there are more atoms for the electrons collide with. Therefore less gets through meaning the current is less so the resistance is increased
Cross-sectional area/width - If the cross sectional area is increased there is more space for the
electrons to move freely making less collisions so more current will
pass through making the resistance decreased. I have done a diagram
below.
Material (resistivity)
What is the difference between AC and DC current?
DC is constant and moves in one direction. AC changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction.
Conductor
Hold electrons loosely so that they can move freely throughout the material
Most metals
Insulator
Holds electrons tightly so that charge stays only in the spot where rubbed
Most non metals
Static electricity
It is not the type of electricity to move around in a path. However when charge is build up it can be discharged
Law of static electricity
- Like charges repel
- Unlike charges attract
- Charges objects attract neutral objects
Grounding
Provides a path for electrons to move from a conductor to a very large object such as the earth
Current (I)
Measure the rate of flow of electrons through a wire (# of electrons past a point/sec) IS MEASURED USING A AMMETER
Unit: amperes/amps (A)
1 amp= 6*10 18 electrons/sec
Voltage (potential difference) (electric potential) (V)
Measure the pressure/force or energy the electrons have. IS MEASURED USING A VOLTMETER
Unit: volts (V)
Series circuit and formulas
electrons only have 1 path to follow
VT= V1+V2+V3…
IT= I1=I2=I3…
Parallel circuit and formulas
electrons have more than 1 path to follow
VT= V1=V2=V3…
IT= I1+I2+I3…
Resistance
Measures the ability of a substance to “resist” the flow of electrons
- resistors are used to control the current and voltage in the circuit to suit the electrical devices in the circuit. this prevents short circuits: too much current flowing through wire or no load to use up energy
Units: ohms
V=IR
