High School Physics : Electricity and Magnetism

Study concepts, example questions & explanations for High School Physics

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Example Questions

Example Question #23 : Resistors

The resistivity of most common metals __________________ . 

Possible Answers:

remains constant over wide temperature ranges

decreases as the temperature increases

varies randomly as the temperature increases

increases as the temperature increases

Correct answer:

increases as the temperature increases

Explanation:

At higher temperature, the atoms are moving more rapidly and are arranged in a less orderly way.  Therefore it is expected that these fast moving atoms are more likely to interfere with the flow of electrons.  If there is more interference in the flow of electrons, then there is a higher resistivity.

 

Example Question #24 : Resistors

Screen shot 2020 08 24 at 8.50.00 am

Which Resistors are connected in parallel?

Possible Answers:

 and 

 and 

None of the answer choices are correct

 and 

All answer choices are correct

Correct answer:

 and 

Explanation:

Resistors are in parallel when the electric current passes through two or more branches or connected parts at the same time before it combines again. After the current leaves the battery it travels to . Then the current splits and travels between the other two resistors before the current coming back together and connecting back to the battery.

Example Question #25 : Resistors

How does adding resistors in parallel affect the overall current of the circuit?

Possible Answers:

The current decreases

The current increases

The current stays the same

Correct answer:

The current increases

Explanation:

Adding resistors in parallel decrease the overall equivalent resistance as they are added using the equation

Since the overall equivalent resistance is decreased, if the voltage is constant the overall current would increase.

Therefore 

This shows the inverse relationship between the two values.

Example Question #26 : Resistors

Screen shot 2020 08 24 at 8.54.25 am

Which resistor has the greatest current going through it?

Assume all the resistors are equal.

Possible Answers:

 and 

 and 

Correct answer:

Explanation:

As we examine the circuit we first come across the first two resistors. These resistors are in parallel. In parallel circuits, the current splits to go down each branch. In this case, the resistors are of equal value meaning that the current is split evenly between the two.

We then come across another parallel branch with two resistors on one side and a single resistor on the other side. The two resistors in series add up to create more resistance on the top branch. The single resistor on its own has less resistance.

Since current always chooses the path of least resistance, more current will flow through the single resistor, than through the branch with two resistors in series.

Therefore,  would have the greatest resistance flowing through it.

Example Question #31 : Circuit Calculations And Concepts

Calculate the current through the 10 ohm resistor.

Possible Answers:

Correct answer:

Explanation:

To begin, let us start with the resistor and the  resistor that are in parallel. In parallel we can add resistors through the equation 

This new resistor is now in series with the two  resistors.  In series we can just add these resistors up.

 

This new resistor is now in parallel with the  resistor. In parallel we can add resistors through the equation 

This new resistor is now in series with the  and  resistor.  In series we can just add these resistors up.

Now that we have the equivalent resistance of the circuit.  We can now determine the current flowing out of the battery.

Rearrange to solve for current.

One of the best ways to work through a problem like this is to create a V= IR chart for all the components of the circuit.


Table1

 

We know that the current that is flowing out of the battery is the current that is flowing through both by 5 and 3 Ohm resistors since all of these are in series.  So we can put this information into our chart.

Table2

 

Using Ohm’s Law we can determine the voltage for each of these two resistors.

 

 Table3

 

We can now use Ohm’s law and our voltage to determine the current going through the 14 Ohm resistor.

 

Table4

Next we can analyze the current in the Junction between the 5, 14 and 4 Ohm resistors.  Kirchoff’s laws state that the sum of the current flowing in and out of junction must equal 0.

 

We have  flowing in from the  resistor and  flowing out to go through the  resistor.

 

So the current going through the 4 Ohm resistor is 3 amps.  This will be the same for both 4 ohm resistors as both have the same current going into and out of the junctions near them.  We can then use this to determine the voltage drop across each of the resistors.

 

 

Now let’s add this to our chart.

Table5

 

We can now use Kirchoff’s loop law to determine the voltage across the 10 Ohm resistor.  Let’s analyze the loop that goes from the 5, to the 4 to the 10 back through the 4 and then through 3 Ohm resistor.

We can now use Ohm’s Law to determine the current through the 10 Ohm resistor.

 

 

 

 

Example Question #1 : Kirchoff's Laws

Calculate the current in the 15 Ohm Resistor.

 

Possible Answers:

Correct answer:

Explanation:

To begin, let us start with the  resistor and the  resistor that are in parallel. In parallel we can add resistors through the equation 

This new resistor is now in series with the two  resistors.  In series we can just add these resistors up.

 

This new resistor is now in parallel with the  resistor. In parallel we can add resistors through the equation 

This new resistor is now in series with the  and  resistor.  In series we can just add these resistors up.

Now that we have the equivalent resistance of the circuit.  We can now determine the current flowing out of the battery.

 

Rearrange to solve for current.

 

 

One of the best ways to work through a problem like this is to create a V= IR chart for all the components of the circuit.

Table1

We know that the current that is flowing out of the battery is the current that is flowing through both by 5 and 3 Ohm resistors since all of these are in series.  So we can put this information into our chart.

Table2

Using Ohm’s Law we can determine the voltage for each of these two resistors.

Table3

We can now use Kirchoff’s loop law through the loop of the 5, 3, and 14 Ohm resistor to determine the voltage that is traveling through the 14 Ohm resistor.

We can now use Ohm’s law and our voltage to determine the current going through the 14 Ohm resistor.

We can now add this information to our chart.

Table4

Next we can analyze the current in the Junction between the 5, 14 and 4 Ohm resistors.  Kirchoff’s laws state that the sum of the current flowing in and out of the junction must equal 0.

 

We have 4A flowing in from the 5 Ohm resistor and 1A flowing out to go through the 14 Ohm resistor.

So the current going through the 4 Ohm resistor is 3 amps.  This will be the same for both 4 ohm resistors as both have the same current going into and out of the junctions near them.  We can then use this to determine the voltage drop across each of the resistors.

Now let’s add this to our chart.

 

Table5

We can now use Kirchoff’s loop law to determine the voltage across the 10 Ohm resistor.  Let’s analyze the loop that goes from the 5, to the 4 to the 10 back through the 4 and then through 3 Ohm resistor.

 

We can now use Ohm’s Law to determine the current through the 10 Ohm resistor.

We can now add this information to our chart.

Table6

 

We can now analyze the junction between the 4, 10 and 15 Ohm resistor.

Kirchoff’s laws state that the sum of the current flowing in and out of the junction must equal 0.

 

We have 2A flowing in from the 4 Ohm resistor and 1.2A flowing out to go through the 10 Ohm resistor.

 

 

 

 

 

 

 

 

 

 

Example Question #2 : Kirchoff's Laws

Calculate the current through the 6 ohm resistor.

 

Possible Answers:

Correct answer:

Explanation:

To begin we need to simplify the circuit to get the equivalent resistance.  Let’s start with the 3 and 6 Ohm resistors in parallel.

 

 

Now we can add this resistor to the 4 Ohm resistor as they are in series.

 

We can now determine the current coming out of the battery using Ohm’s Law.

 

Rearrange to solve for current.

 

The current coming out of the battery will be the same current that moves through the 4 Ohm resistor.  So we can determine the voltage drop across the 4 ohm resistor.

 

We can then use Kirchoff’s loop law to determine the voltage drop across the 6 Ohm resistor.  Let’s analyze the loop that goes from the battery to the 4 ohm resistor and through the 6 ohm resistor.

 

Example Question #81 : Electric Circuits

Calculate the voltage drop across the 4 ohm resistor.

 

Possible Answers:

Correct answer:

Explanation:

To begin we need to simplify the circuit to get the equivalent resistance.  Let’s start with the 3 and 6 Ohm resistors in parallel.

 

Now we can add this resistor to the 4 Ohm resistor as they are in series.

 

We can now determine the current coming out of the battery using Ohm’s Law.

 

Rearrange to solve for current.

The current coming out of the battery will be the same current that moves through the 4 Ohm resistor.  So we can determine the voltage drop across the 4 ohm resistor.

 

 

Example Question #82 : Electric Circuits

Kirchoff’s junction rule is an example of 

 

Possible Answers:

Conservation of momentum

Conservation of charge

None of the givens answers

Conservation of energy

Correct answer:

Conservation of charge

Explanation:

Kirchoff’s loop rules states the sum of the current going into and out of the junction must equal 0. In other words, the current going in must equal the current going on.  Current is a measure of the flow of charge.  Therefore, this law is conservation of charge as the number of electrons going into a junction must equal the number of electrons flowing out.

 

Example Question #83 : Electric Circuits

 

Calculate the voltage drop across the 14 ohm resistor.

 

Possible Answers:

Correct answer:

Explanation:

To begin, let us start with the  resistor and the  resistor that are in parallel. In parallel we can add resistors through the equation 

This new resistor is now in series with the two 4Ω resistors.  In series we can just add these resistors up.

 

This new resistor is now in parallel with the  resistor. In parallel we can add resistors through the equation 

This new resistor is now in series with the  and  resistor.  In series we can just add these resistors up.

Now that we have the equivalent resistance of the circuit.  We can now determine the current flowing out of the battery.

 

Rearrange to solve for current.

One of the best ways to work through a problem like this is to create a V= IR chart for all the components of the circuit.


Table1

We know that the current that is flowing out of the battery is the current that is flowing through both by 5 and 3 Ohm resistors since all of these are in series.  So we can put this information into our chart.

Table2

 

Using Ohm’s Law we can determine the voltage for each of these two resistors.

 Table3

We can now use Kirchoff’s loop law through the loop of the 5, 3, and 14 Ohm resistor to determine the voltage that is traveling through the 14 Ohm resistor.

 

 

 

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