Electricity and Magnetism
Help Questions
Physics › Electricity and Magnetism
The current in a circuit is and the voltage is
. What is the resistance?
Explanation
Ohm's law says . Plug in our given values to solve.
Three capacitors of equal capacitance are in a series circuit. If the total capacitance is , what is the capacitance of each individual capacitor?
Explanation
The formula for capacitors in a series is:
Since we have three equal capacitors, we can say:
Using the value for total capacitance, we can find the value for the individual capacitance.
The current in a circuit is and the voltage is
. What is the resistance?
Explanation
Ohm's law says . Plug in our given values to solve.
What is the net resistance of the circuit connected to the battery?
Explanation
To find the net resistance of the circuit, we must summarize all of the different resistors, one piece at a time. To begin, let’s start with the two resistors in the upper left had corner which are in series. In series resistance can be added together. We can replace these two resistors with a single resistor that is valued at .
Next, this new resistor is in parallel with the resistor that is on the diagonal line from point A to point B. In parallel we can add resistors through the equation
This new resistor is now in series with the resistor that is between points B & C. In series we can just add these resistors up.
This new resistor is now in parallel with the resistor that is between points A & C. In parallel we can add resistors through the equation
This new resistor is now in series with the resistor that is between the battery and point C. In series we can just add these resistors up.
What is the voltage of a circuit with of current and
of resistance?
Explanation
For this problem, use Ohm's law: . In this equation
is the voltage,
is the current, and
is the resistance.
Plug in the given values and solve for the voltage.
The direction of conventional current is taken to be the direction that __________________ .
negative charges would flow
positive charges would flow
Explanation
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.
Why might a circuit breaker open if you plug too many electrical devices into a single circuit?
The voltage becomes too high
The current becomes too high
The resistance becomes too high
A circuit breaker will not “trip” no matter how many electrical devices you plug into the circuit
Explanation
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.
Which of the equations here is valid for the circuit shown?
Explanation
To answer this question we must consider Kirchoff’s Loop Law. This law states that the voltage around any loop must equal 0. In this case there are two different loops at play. To begin, let’s start on the left with the 2 Volt battery.
As we start with the 2 Volt battery, we then move into the 1 Ohm resistor with going through it. Ohm’s law states that the voltage is equal to the current times the resistance. Therefore the voltage through this circuit is
Since this resistor is using the voltage this will be a negative voltage when we sum around the loop.
We will continue our loop through the middle of the circuit into the 4 Volt battery. This battery is facing the opposite direction from our 2 Volt battery and therefore will be a negative when it comes to our equation.
Next is the 2 Ohm resistor with going through it. According to Ohm’s law the voltage being used by this resistor is equal to
When summarizing all of these parts we get an equation that looks like which simplifies down to
This is one of the equations available to us and therefore there is no need to analyze any other loops.
Materials in which the electrons are bound very loosely to the nuclei and can move about freely within the material are referred to as
Insulators
Conductors
Semiconductors
Superconductors
Explanation
Conductors allow the electrons to flow freely along it. That is why metal; is considered a good conductor. It allows the electrons to flow through it which is why it is used in wire in an an electric circuit.
Which of the equations here is valid for the circuit shown?
Explanation
To answer this question we must consider Kirchoff’s Loop Law. This law states that the voltage around any loop must equal 0. In this case there are two different loops at play. To begin, let’s start on the left with the 2 Volt battery.
As we start with the 2 Volt battery, we then move into the 1 Ohm resistor with going through it. Ohm’s law states that the voltage is equal to the current times the resistance. Therefore the voltage through this circuit is
Since this resistor is using the voltage this will be a negative voltage when we sum around the loop.
We will continue our loop through the middle of the circuit into the 4 Volt battery. This battery is facing the opposite direction from our 2 Volt battery and therefore will be a negative when it comes to our equation.
Next is the 2 Ohm resistor with going through it. According to Ohm’s law the voltage being used by this resistor is equal to
When summarizing all of these parts we get an equation that looks like which simplifies down to
This is one of the equations available to us and therefore there is no need to analyze any other loops.