Concept 1 Practice
List the 3 subatomic particles, their charges, and where they are located in an atom.
Electrons - Very small, negatively charged and are in constant movement around the nucleus (center of atom)
Protons - Larger, positively charged and they remain stationary in the nucleus of the atom
Neutrons - Similar in size to protons but have NO charge and are stationary in the nucleus
Explain how a battery works
Chemical reactions in the middle band create positive and negative ions and stores the + and - sides of the battery called terminals.
Dry Cell Batteries - Chemical reaction in the moist paste causing the separation of + and -
Wet Cell Batteries - Metal plates in a chemical solution that transfers e- from plate to plate
Differentiate between the effects of an open vs. closed circuit
- Open current can't flow
- Closed current can flow
Describe the three rules of charge.
1. Opposite charges attract
2. Like/similar charges repel
3. All charges are conserved
Four factors that affect resistance
1. Materials - Insulators have more resistance than conductors. All materials have some resistance
2. Size of Wire - The thickness of the diameter of the wire affects the resistance. The smaller the diameter, the fewer e- flow and resistance increases
3. Length of Wire - The longer the wire, the more resistance to e- flow
4. Temperature of Wire - Higher temperatures creates greater resistance
Draw a series circuit with one battery, a 2 ohm resistor, a light bulb, and a switch to turn the whole circuit off
Three ways charge can be transferred
1. Conduction - transfer through direct contact
2. Friction - transfer through rubbing contact that brushes off e- from one object to another
3. Induction - Rearrangement of e- on a neutral object by an electric field of nearby charged objects
Explain the relationship between voltage, current, and resistance in a circuit
The amount of current is directly proportional to the voltage difference and inversely proportional to the resistance
Draw a parallel circuit with two batteries, 3 light bulbs, switches to turn each light off, and a switch to turn the whole circuit off
Examples of good conductors and good insulators
Conductors - Metals (especially copper), skin, water
Insulators - Plastic, wood, air, rubber, glass, styrofoam
Calculate the current flowing through the circuit of a toy car that has a resistance of 20 ohms and is powered by a 3 volt battery.
I = 3/20
I = 0.15 amps
Calculate the voltage difference of a battery that is part of a series circuit with a current of two amps. Also on the circuit are a 2 ohm resistor and a light bulb that has a resistance of 1 ohm.
Rt = 2 + 1 = 3 ohms
V = 2 x 3
V = 6
How does lightning work?
Movement of clouds causes build up of static electricity in clouds.
When e- build up enough, it induces a (+) charge on Earth.
Attraction becomes great enough e- travel from the clouds to Earth to neutralize.
Calculate the voltage difference in a circuit with a resistance of 25 ohms if the current is 0.5 amps
0.5 = V/25
0.5 x 25 = V
V = 12.5
Find the total resistance in a parallel circuit with a 100 ohm resistor, a 50 ohm resistor, and a 25 ohm resistor
1/Rr = 1/100 + 1/50 +1/25 (find common denominator, then add)
1/Rr = 7/100 (flip to 100/7, then divide)
RT = 14.3 ohms