High School Physics : Electricity and Magnetism

Study concepts, example questions & explanations for High School Physics

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Example Questions

Example Question #936 : High School Physics

What is the main difference between electrical and gravitational forces?

Possible Answers:

Gravitational forces are always attractive but electrical forces can be attractive or repulsive

Gravitational forces obey the inverse square law and electrical forces do not

Electrical forces obey the inverse square law and gravitational forces do not

Electrical forces attract and gravitational forces repel

Correct answer:

Gravitational forces are always attractive but electrical forces can be attractive or repulsive

Explanation:

Electric forces can be attractive or repulsive because charges may be positive or negative. In the case for gravitational forces, there are only attractive forces because mass is always positive.

 

Example Question #937 : High School Physics

What is the magnitude of force a   charge exerts on a  charge  away?

Possible Answers:

Correct answer:

Explanation:

We can calculate this using Coulomb’s Law

 

Example Question #938 : High School Physics

When the magnitude of two interacting charges is increased by a factor of 2, the electrical forces between these charges is __________. 

Possible Answers:

reduced by a factor of 4

reduced by a factor of 2–√

quadrupled

doubled

reduced by a factor of 3

Correct answer:

quadrupled

Explanation:

In Coulomb's law, an increase in both interacting charges will cause an increase in the magnitude of the electrical force between them. Specifically if the magnitude of both interacting charges is doubled, this will quadruple the electrical force.

Example Question #939 : High School Physics

Screen shot 2020 08 07 at 2.43.17 pm

At each corner of square of side  there are point charges of magnitude Q, 2Q, 3Q and 4Q.  Determine the magnitude and direction of the force on the charge 3Q.

Possible Answers:

 away from the other charges

  away from the other charges

 toward Q

 toward Q

Correct answer:

  away from the other charges

Explanation:

We will need to use Coulomb’s Law to analyze the force on the 3Q charge from all the other forces.  We will then summarize the net force in the  and  direction to determine the force on the 3Q charge.

 

In the x-direction

 

Force from 4Q on 3Q

 

Force from Q on 3Q in the x direction

 

Add these together in the x-direction 

 

 

 

In the y-direction

 

From from 2Q on 3Q

 

 

Force from Q on 3Q in the y direction

 

 

Add these together in the y-direction 

 

 

 

Now we can find the resultant of these sides using the Pythagorean theorem.

 

 

 

 

 

 

 

 Screen shot 2020 08 07 at 2.43.54 pm

Example Question #1 : Understanding Electricity

What is the maximum power consumption of  portable CD player that draw a maximum of  of current?

Possible Answers:

Correct answer:

Explanation:

The power in a circuit is equal to the current times the voltage.

 

Example Question #941 : High 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

 

Possible Answers:

Current

Voltage

Electric potential

Wattage

Correct answer:

Current

Explanation:

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

Possible Answers:

Increase by a factor of two

Increase by a factor of four

Decrease to one fourth its original value

Decrease to one half its original value

Correct answer:

Decrease to one half its original value

Explanation:

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

 

 

 

We know that

 

So we can substitute this value in

 

 

And solve for 

 

 

Therefore the power would be cut in half.

 

Example Question #3 : Understanding Electricity

A current of  flow in a wire.  How many electrons are flowing past any point in the wire per second? 

Possible Answers:

Correct answer:

Explanation:

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 #4 : Understanding Electricity

The direction of conventional current is taken to be the direction that __________________ .

Possible Answers:

positive charges would flow

negative charges would flow

Correct answer:

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.

Example Question #5 : Understanding Electricity

Why might a circuit breaker open if you plug too many electrical devices into a single circuit?

Possible Answers:

The current becomes too high

The voltage 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

Correct answer:

The current becomes too high

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.

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