All High School Physics Resources
Example Questions
Example Question #51 : Electric Circuits
What is the maximum power consumption of portable CD player that draw a maximum of of current?
The power in a circuit is equal to the current times the voltage.
Example Question #81 : Electricity And Magnetism
The total amount of charge that passes through a wire’s full cross section at any point per unit of time is referred to as
Current
Voltage
Electric potential
Wattage
Current
Current is defined as the amount of charge that passes through a specific area of a wire in a specific interval of time. It is measured in Amps which are Coulombs per second.
Example Question #53 : Electric Circuits
If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit
Decrease to one fourth its original value
Increase by a factor of two
Decrease to one half its original value
Increase by a factor of four
Decrease to one half its original value
Decrease to one half its original value
The equation for Power is
According to Ohm’s Law
We can rearrange this equation for current as this is what is changing in our circuit.
We can then substitute this back into the power equation.
If we have the original value
and our second value
We can rearrange both for the voltage and set them equal to each other
,
So we can substitute this value in
And solve for
Therefore the power would be cut in half.
Example Question #82 : Electricity And Magnetism
A current of
flow in a wire. How many electrons are flowing past any point in the wire per second?
The current is a measure of the amount of charge that passes a given point in a certain amount of time.
To determine how many electrons are passing this point we need to look at the charge of 1 electron and do a conversion.
Example Question #83 : Electricity And Magnetism
The direction of conventional current is taken to be the direction that __________________ .
positive charges would flow
negative charges would flow
positive charges would flow
We often think of current flowing from the top of the battery to the bottom of the battery. The top of the battery has a higher electrical potential than the bottom of the battery and is associated as being positive. Charges interact in such a way where like charges repel and opposite charges attract. Since we think of the charges traveling away from the positive end of the battery and toward the negative end of the battery, this would model the motion of a positive charge (away from positive and toward negative). Since it is not protons that move through the circuit, but rather electrons. It is more accurate to describe the flow of electrons from the negative side of the battery to the positive side.
Example Question #1 : Understanding Electricity
Why might a circuit breaker open if you plug too many electrical devices into a single circuit?
The current becomes too high
A circuit breaker will not “trip” no matter how many electrical devices you plug into the circuit
The voltage becomes too high
The resistance becomes too high
The current becomes too high
When plugin objects into a single circuit, these objects are connected in parallel as each one will receive the 120V from the electrical outlet. However, as additional objects are added, the current is thereby increased. Circuit breakers are designed to trip once the current reaches a maximum load and shuts down the circuit to protect the wires, and the devices that are plugged into the circuit as high current can damage these devices.
Example Question #1 : Understanding Electricity
A 4.5V battery is connected to a bulb whose resistance is
. How many electrons leave the battery per minute?
electrons
electrons
electrons
electrons
electrons
We first need to determine the current coming through the bulb. We can use Ohm’s law to determine this.
Current by definition is the amount of charge per unit time.
We are looking at the number of electrons in one minute which is 60 seconds.
We now know the amount of charge passing through in 60 seconds. We know that the charge of the electron is
. We can use this to figure out how many electrons are going through.
Example Question #91 : Electricity And Magnetism
Nothing happens when birds land on a power line, yet we are warned not to touch a power line with a ladder. What is the difference?
Birds have extremely high internal resistance compared to humans
Most birds don’t understand the situation
There is little to no voltage drop between a bird's two feet, but there is a significant voltage drop between the top of a ladder touching a power line and the bottom of the ladder on the ground
Dangerous current comes from the ground only
There is little to no voltage drop between a bird's two feet, but there is a significant voltage drop between the top of a ladder touching a power line and the bottom of the ladder on the ground
Electricity travels from the point of highest potential to the lowest potential. We measure the difference between these two potentials as the voltage. Since both of the birds' feet are on the wire, both feet have the same potential. However, if the ladder touches the power line and the bottom of the ladder is on the ground, there is a much higher potential difference (as the ground is at 0 potential). Therefore the electricity will travel down the ladder!
Example Question #92 : Electricity And Magnetism
When a light switch is turned on, the light comes on immediately because
The electrons already in the wire are instantly “pushed” by the voltage difference
The electrons coming from the power source move through the initially empty wires very fast
The lightbulb may be old with low resistance. It would take longer if the bulb were new and had high resistance
The electricity bill is paid. The electric company can make it take longer when the bill is unpaid
The electrons already in the wire are instantly “pushed” by the voltage difference
It's kind of like when you turn on the faucet; the water doesn't have to travel from the water tower to your house before it starts flowing. Similarly, the electrons are always in the circuit. Once the switch is turned on, there is a voltage difference present, which is what then pushes these electrons through the circuit (like turning on the faucet).
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