Physics #3
How would you define electricity?
The flow of charges within a circuit; a continuous conducting circuit.
Conductors on a light bulb?
Threaded section, filament, tip and support wire.
Current
*Not a speed, VOLUME Symbol: I Units: Amps
What % voltage should you get with a wire?
0%
Name two ways to increase the resistance in a parallel circuit?
1. Decrease the voltage 2. Remove resistors (opposite to series because when you added second bulb in parallel, there's more deflection because there's an increase in current)
What are the five steps?
1. Diagram the circuit using the appropriate symbols; draw the current path. 2. Inventory- list your givens are unknowns 3. Choose the appropriate equation (rearrange if necessary) 4. Plug in all values wit their unites 5. Solve and round final answers to correct # of sig figs
Imagine there are three resistors in a series circuit; they are a 25 ohm, 40 ohms, and a 75 ohm. If they are connected to a 110 volt battery, find the power generated by 75 resistor
47 watts
In these four circuits: -Series circuit with round bulb and then long bulb -Series circuit with long bulb and then long bulb -series circuit with two round bulbs -Parallel circuit with two round bulbs ————————————————————————————————- Which of the above circuits had the largest total/overall resistance
A and B, order doesn't matter
What materials and conditions must be present for a bulb to light?
A closed continuous conducting path, and something to initiate the charge.
How does a fuse protect a circuit?
A fuse is a low resistance wire which will melt if the current is too strong. The fuse melts and breaks the circuit. This stops the electric current and prevents fires or other safety hazards.
When does something have low resistance?
A resistor that allows charge to go through easily has low resistance
Definition of circuit?
Any unbroken loop or electrical components that form a continuous conducting path
What happens in a circuit with three round bulbs in series?
Compass deflection lowers compared to circuit with one round bulb and a circuit with two round bulbs, and bulbs dim compared to circuit with one bulb and a circuit with two round bulbs.
What happens in a circuit with two round bulbs in series?
Compass deflection lowers compared to circuit with one round bulb, and bulbs dim compared to circuit with one bulb.
In these four circuits: -Series circuit with round bulb and then long bulb -Series circuit with long bulb and then long bulb -series circuit with two round bulbs -Parallel circuit with two round bulbs ————————————————————————————————- Which of the above circuits produced the brightest light?
D
In these four circuits: -Series circuit with round bulb and then long bulb -Series circuit with long bulb and then long bulb -series circuit with two round bulbs -Parallel circuit with two round bulbs ————————————————————————————————- Which of the above circuits produced the larges current amount
D
In these four circuits: -Series circuit with round bulb and then long bulb -Series circuit with long bulb and then long bulb -series circuit with two round bulbs -Parallel circuit with two round bulbs ————————————————————————————————- Which of the above circuits showed the greatest compass deflection amount?
E- because there's the least resistance
A series circuit contains a generator, an ammeter and a light bulb, the current in a light bulb is
Equal everywhere
T/F (IN SERIES): bulb A used up some moving charge so ess reaches bulb B
F: Bulb A doesn't use up....same amount reaches bulb B
T/F (IN SERIES): when the circuit is connected, bulb A lights before bulb B
F: bulb A lights at the same time
T/F (IN SERIES): Bulb B will be brighter than lube C
F: exactly as bright
T/F (IN SERIES): a battery is needed to light the bulbs because it is the source of the moving charge
F: it is the push of the energy
Why is flow rate different than speed?
Flow rate is not the same idea as speed. ————————————————————————- Flow rate refers to net amount of charge per second passing through part of a circuit. ——————————————————————————— Speed refers to distance traveled per second by a small bit of charge.
What's the rule for a parallel circuit?
For parallel connections, the moving charge is split into parts. Each part will pass through only one resistor, so its motion will be resisted only once.
What relationship did George Ohm find to be true for certain conductors?
He found that the ratio of potential difference to current is a constant value for certain conductors, which means the resistance value of the conductor stays constant (R= V/I)
List the correct symbols and unit or current, potential difference and resistance
I= Amps V= Volts R= Ohm
In a series circuit, what happens if a bulb goes out?
If one bulb goes out, the whole thing goes out.
What happens if the battery is reversed?
If the battery is reversed, the direction of the charge flow is also reversed.
Using ohm's law, describe 2 ways you can change or control the amount of current that flows in a circuit
If you add more bulbs then you can limit the amount of resistance to control or change the current amount. —————————————————————————————————————————————————————————————————- Adding more batteries raises the potential difference, which raises the current.
(In a parallel circuit, when you add Bulb C in parallel with bulb B) —————————————————————————————————————- When bulb C is added, the compass needle deflection
Increased
If you were to graph the relationship between potential difference vs. current, what type of line/relationship would it produce?
Linear/direct; positive slope
How does deflection and bulb brightness relate to resistance?
More deflection = less resistance Dimmer bulb= more resistance Therefore Less deflection = dimmer bulb
Equation for Power?
P= V(I) P= (V^2/R) P= I^2 (R) V= square root of (P)(R)
What is the role of a battery in a circuit?
Provides the energy source ———————————————— Maintain the potential difference between 2 points ——————————————— Reenergizes the charges ——————————————— Controls direction of the current
How to find the total resistance in a circuit?
R total = R1+R2....etc
Ohms Law Equations:
R= V/I I= V/R V= R(I)
(In a parallel circuit, when you add Bulb C in parallel with bulb B) —————————————————————————————————————- When bulb C is added, the brightness of bulb B
Remains the same
All electrical devices are
Resistors
Definition of an insulator?
Something that prevents the bulbs from lighting
Voltage/ Potential Difference
Symbol: V Units: Volts
T/F (IN SERIES): charge flows at the same rate through bulb A and B
T
T/F (IN SERIES): if bulb C is removed from it's socket, bulb A will go out
T
What is the Voltage drop?
The amount of voltage used or lost through any conductor in the process of moving the current through that part of the circuit.
What does the battery do when the bulbs are lit?
The battery is jumpstarting the motion of the charge throughout the entire circuit.
In a parallel circuit, when you add Bulb C in parallel with bulb B, what happens to the charge flow?
The charge flow increased
Considering the conducting parts of the socket, and the conducting parts of a light bulb, explain why the socket is designed the way it is.
The charge travels through the threaded section, a conductor, and into the two wires and filament, also conductors.
In a series circuit, what is the rule with current?
The current is the same everywhere in the circuit (i.e. all of the resistors get access to the entire amount)
What happens in a circuit with two round bulbs vs a circuit with just one round bulb?
The deflection lowers and the bulbs dim, so there is less flow rate (?)
If you have a break in the parallel circuit, what happens?
The other light will stay lit.
What is the relationship between the resistance value of a resistor and the amount of voltage it gets from the circuit?
There is a direct/linear relationship between the Resistance value (ohms) of a resistor and the amount of Voltage it gets from the circuit (Vdrop) ——————————————————————— As Vdrop increases, R increases an vice versa
T or F: Compass deflection goes up and down together with bulb brightness.
True
What is the equation for Vdrop?
Vdrop + I*R (individual value)
What do conductors do?
Very good at allowing charge flow
What do insulators do?
Very good at blocking charge flow
What is potential difference?
Voltage - a form of energy that pushes the electric charge around the circuit ——————————————————————————————————— also refers to the differences in potential energy between two points.
What is a resistor?
a device having resistance to the passage of an electric current.
How can you find the total current in a series circuit?
can be found using Ohms law equation and substituting in the value of Req —————————————————————- Req= R1+R2+R3
What happens when an energy source (such as a battery) runs down or "dies"
it can no longer sustain two different energy levels at it's opposite ends if poles- there is no more push or force left.
When does something have high resistance?
one that is "a harder place for charge to get through" has high resistance.
Voltage (potential difference)
refers to the amount of energy supplied per charge that moves or "pushes" charges from one point in a circuit to another; also refers to the differences in potential energy between two points.
Power:
refers to the rate at which work is done. ————————————————————————— performed by a device, it measures the rate at which energy is transferred; ————————————————————————— it is affected by voltage, current and resistance. ————————————————————————— Measured by Watts, (W) Symbol P
Energy:
the ability to do work; to complete some type of task.
Ohm's Law
the ratio of potential difference to current is a constant value for certain conductors; this means the resistance value of the conductor stays constant.
What experiments suggest that wires have essentially zero resistance?
• Adding more wire in the series with a lit bulb did not change the brightness of the bulb, so the wire must have little or no resistance. • Shorting out a bulb causes a second bulb in a series to become much brighter, so the wire has much less resistance than the shorted out bulb.
Connect an alligator clip to one side of the socket. Tap the other end on the other side of the socket very briefly, and observe what happens. Based on your observations, what do you think the extra wire is doing?
• Brightness increased in one bulb and compass deflection increased on bursts. Maybe the additional tap wire acted as a detour for the current; easier passes for the charges vs. another filament.
when more bulbs are added to the circuit, is there always more total resistance as a result?
• No, if more bulbs are added in a series, the total resistance increases. But if more bulbs are added in a parallel, there is less total resistance.
How are round bulbs and long bulbs made?
• Round bulb: filament much longer and thicker in length • Long bulb: filament is much thicker and coiled tighter
In what way do you think bulb filaments influence movement of charge in a circuit?
• The bulb filaments partially block the charge in the circuit causing the light to become more dim.
Which has the thickest filament- a high resistance bulb or a low resistance bulb?
• The lower resistance bulb has a thicker filament thicker because it has more space to travel through (the wire).
How is a light bulb like a resistor?
• They are places where charge is difficult to flow through
What happens when you have two batteries?
Add up their voltages
In a series circuit that originally contained two bulbs, you add bulb c IN SERIES ———————————————————— Compass needle deflection
Decreased
In a series circuit that originally contained two bulbs, you add bulb c IN SERIES —————————————————————— Charge flow through the battery
Decreased
In a series circuit that originally contained two bulbs, you add bulb c IN SERIES ————————————————— When bulb C is added, what happened to brightness of bulb A?
Decreased/dimmed
What happens in a circuit if there's a round bulb, and then a long bulb in series?
Deflection gets smaller and the round bulb doesn't light. —————————————————————Long bulb lights but is dimmer than a circuit with just one round bulb.
What happens in a circuit if you have a long bulb and then a short bulb in series?
Deflection lessens from a circuit with one round bulb but stays the same as a circuit with a round bulb, and then a long bulb in series. ——————————————————————
In circuits with parallel resistance,
Draw multiple arrows
(In a parallel circuit, when you add Bulb C in parallel with bulb B) —————————————————————————————————————- When bulb C is added, the rate of charge flow through the battery
Increased
What do conductors have in common?
Most of them are metallic
Conductor defintion
Something that permits the bulbs to light
Resistance
Symbol: R Units: Ohm/ Greek symbol
(In a parallel circuit, when you add Bulb C in parallel with bulb B) ————————————————— If bulb C is removed from it's socket:
Bulb B will remain lit
(In a parallel circuit, when you add Bulb C in parallel with bulb B) ———————————————————————————————— Will bulb B be dimmer or brighter?
Bulb b will be the same brightness as bulb C (ASK WHY)
What are two types of observations that can be used to indicate flow rate?
Bulb brightness and compass deflection
What is bulb lighting caused by?
Bulb lighting is caused by all the charge passing through the filament.
In a series circuit, what happens to the charge flow?
Charges align themselves based on what the highest resistance/hardest thing to go through. Then that charge flow stays the same throughout.
What happens if you add a round bulb in parallel with a circuit that previously only had one round bulb? If that makes zero sense: you had a circuit with one round bulb and now it has two in parallel
Compass deflection increased, and bulb brightness decreased
