高School Physics : Understanding Electricity
Study concepts, example questions & explanations for High School Physics
Example Questions
Example Question #931 :高School Physics
What is the maximum power consumption of
The power in a circuit is equal to the current times the voltage.
Example Question #941 :高School Physics
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
Electric potential
Current
Voltage
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 #2 :Understanding Electricity
If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit
Increase by a factor of four
Increase by a factor of two
Decrease to one half its original value
减少到原来的四分之一的价值
Decrease to one half its original value
Decrease to one half its original value
The equation for Power is
According to Ohm’s Law
我们可以重新安排这个方程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
We can rearrange both for the voltage and set them equal to each other
We know that
So we can substitute this value in
And solve for
Therefore the power would be cut in half.
Example Question #61 :Electric Circuits
A current of
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 #1 :Understanding Electricity
The direction of conventional current is taken to be the direction that __________________ .
negative charges would flow
positive 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 #61 :Electric Circuits
Why might a circuit breaker open if you plug too many electrical devices into a single circuit?
The voltage becomes too high
A circuit breaker will not “trip” no matter how many electrical devices you plug into the circuit
The resistance becomes too high
The current 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 #64 :Electric Circuits
A 4.5V battery is connected to a bulb whose resistance is
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
Example Question #65 :Electric Circuits
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
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
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 #2 :Understanding Electricity
When a light switch is turned on, the light comes on immediately because
The electrons coming from the power source move through the initially empty wires very fast
The electrons already in the wire are instantly “pushed” by the voltage difference
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).
