MATH REVIEW VIDEOS

This website can help you review the basic math questions asked on the test.

www.khanacademy.org

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1.  www.edx.org

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QUESTIONS FOR THE DAY

1. Which of the following will occur if a positively charged rod is brought close to the plate of an electroscope.
A. The gold leaves will move closer together.
B. The gold leaves will move move apart.
C. The gold leaves will not move at all.

2. Which of the following will occur if a negatively charged rod is brought close to the plate of an electroscope.
A. The gold leaves will move closer together.
B. The gold leaves will move move apart.
C. The gold leaves will not move at all.

3. Which of the following will occur if a positively charged rod is brought close to the plate of an electroscope.
A. The positive charges will be attracted to the plate.
B. The negative charges will be attracted to the plate.
C. The gold leaves will move closer together.

4. Which of the following will occur if a negatively charged rod is brought close to the plate of an electroscope.
A. The positive charges will be attracted to the plate.
B. The negative charges will be attracted to the plate.
C. The gold leaves will move closer together.


Answers:   1.  B        2.  B        3.  B        4.   A  

THE ELECTROSCOPE

The electroscope is a device used to determine the presence and magnitude of charges. That is, it helps you to determine whether on object is charged or not. It also helps you to determine the type of charge.
You can easily make an electroscope at home. Click here to see a simple electroscope.

CHARGING OF MATTER

An object is said to be charged when it gains or loses an electron. There are three ways to charge matter. 

• Charging by friction
• Charging by contact 
•  Charging by induction

Charging by Friction: When you rub two non-conducting materials on each other, they are charged by friction. The material that loses the electron is positively charged and the one that gains the electron is negatively charged. The amount of electrons gained and lost is equal to each other. Example: When a glass rod is rubbed on silk, the glass rod loses electrons and becomes positively charged while the silk gains electrons to become negatively charged.

Charging by Contact: When a charged object comes into contact with a neutral material, the charge on the charged object is transfer to the neutral one.

Charging by induction: Consider two conductors, A and B, that are neutral at the beginning. 

___________________

        A                B           

When a positively charged plate is brought near them, it attracts the electrons in the conductors.

               +                      A               B           

 Electrons move to the left part and protons stays. 

      +                  --    A               B     ++      

When  plates A and B are separated they are charged by induction. Note that is no contact between the positively charged plate and the two conductors. They are charged only by induction and conductor  A becomes  negatively charged and B becomes positively charged.

    --    A                              B     ++      

This is a link to an animation on charging an electroscope.