The Electroscope
Detecting electric charge and observing electron movement
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Electroscope
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B. Detecting Electric Charges.
1. Electroscope - used to detect presence of a charged object.
a) If no charge is present, leaves point straight down.
b) leaves separate in presence of charge.
c) Transfer of charge
1. Charge can be transferred between neutral objects by friction.
Ex) hard rubber rod rubbed with fur or wool causes electrons to be transferred to rod.
Rubber Rod - gains electrons
Becomes Negative
wool or fur
Becomes Positive
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. What is an electroscope used for?
2. The leaves of a charged electroscope spread apart. Why?
3. A hard rubber rod is rubbed with fur. What charge does the rod get?
4. After rubbing a rubber rod with fur, what is the charge of the fur?
5. When a hard rubber rod is rubbed with wool, where does the rod's charge come from?
Identifying an Unknown Charge
A student has an electroscope that is already negatively charged, so its leaves are spread apart. She uses it to test the charge on several rods by bringing each rod near the top of the electroscope without touching it.
When rod X is brought near, the leaves spread farther apart. What is the charge on rod X?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. A neutral electroscope has a charged rod brought near its top. What happens to its leaves?
C2. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C3. Place a check mark in three boxes to indicate the actions that would cause the leaves of this negatively charged electroscope to move closer together.
C4. The electroscope has a charge of −8.0 × 10−10 C. Substitute numerical values into a mathematical representation that can be used to determine the number of excess electrons on the electroscope. Then calculate the number of excess electrons.
C5. Why are electroscope leaves made of very thin metal foil?
C6. Describe a procedure that uses this negatively charged electroscope to classify an unknown rod as negative, or as positive-or-neutral. Identify the observation that gives a definite result, and explain why the other observation is not definite.