Induction
Positive Rod

Positive Induction lesson illustration

What rule big rule of static electricity
explains why her hair is like this?

Positive Induction lesson illustration

www.bnl.gov

NOAA Photo Library

Enrichment

Positive Induction lesson illustration

Read About Faraday Cages in Wikipedia

A metal cage creates a shield against
very strong electric fields

University of Tehran High Voltage Lab. Person in cage: Prof. H.Mohseni

School blocks YouTube?
Use the file below.

Faraday_Cage.mov

Faraday Cage Protects from 100,000 V

Physikshow of the University of Bonn

Here's how it works

Positive Induction lesson illustration

Stanisław Skowron

Conduction
Fill in the Blank Notes

3. Induction - Positive Rod

[ Flash ]

No charge is transferred

Electrons redistributed

Induction with a Positive Rod

Positive Induction lesson illustration

Frame 1 - Neutral Electroscope

[ Flash ]

#p = #e-

Frame 2 - Rod comes near

[ Flash ]

Charge on electroscope?

#p = #e-

Electroscope is neutral

Charge of Knob (top)?

Negative

[ Flash ]

Charge of Leaves?

Positive

Frame 3 - Rod Removed,
Charges Return

[ Flash ]

Electroscope is neutral

"What would happen
to the leaves of this electroscope if a
positively charged rod
were brought near the
top of the electroscope?"

Positive Induction lesson illustration

"Electrons would be
attracted up from leaves toward positive rod.
Leaves would become
more positive and
diverge more."

"Which graphic shows

the electron distribution

of a neutral electroscope

near a positive rod?"

Positive Induction lesson illustration

Choice 4

Positive Induction lesson illustration

"Electrons are attracted up towards the positive rod"

Enrichment

Positive Induction lesson illustration

Like a Bird on a Wire

Electricity, Height and Women

Clip from Straight Up:
Helicopters in Action from David Douglas on Vimeo.

Segment from the helicopter documentary "Straight Up!", showing power line
maintenance being performed on live wires by a man outside a helicopter, using a type of Faraday cage.

Like_a_Bird_on_a_Wire.mov

Check Your Understanding

5 quick questions — pick an answer to see if you’re right.

1. A positive rod is held near the knob of a neutral electroscope. What is the knob's charge?

2. In the same situation, what is the charge of the leaves, and what do they do?

3. When the positive rod is removed without ever touching, the electroscope is

4. A positive rod is brought near the top of an electroscope that is already positive. What happens to the leaves?

5. A person inside a metal Faraday cage is unharmed by a huge spark outside. What does the cage do?

NYSSLS Regents Practice · Electricity · Positive Induction

Inducing a Negative Charge

A positively charged rod is held near (not touching) a neutral metal sphere. The sphere is grounded briefly while the rod is near, the ground connection is removed, and then the rod is taken away.

What is the final charge on the sphere, and how did it get that charge?

▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)

Challenge score: 0 / 6

Substitute values

C1. During grounding, 2.0 × 10¹⁰ electrons flow from Earth onto the sphere. Substitute numerical values into a mathematical representation that can be used to determine the magnitude of the sphere’s final charge. Then calculate the charge.

q = ( × 10¹⁰)( × 10⁻¹⁹ C) = × 10⁻⁹ C

Multiple choice

C2. While the rod is near (before grounding), which side of the sphere is negative?

Select all that apply

C3. Place a check mark in three boxes to indicate the statements that correctly describe this charging-by-induction process.

The rod touches the sphere. Electrons flow from Earth through the ground wire onto the sphere. Protons flow from the sphere into Earth. The rod’s charge stays the same. Electrons flow from the rod to the sphere. The ground is removed while the rod is still near the sphere.

Support or Refute · Justify

C4. A student makes the following claim.

Claim: After the process is complete, Earth has a slightly negative charge.

Place a check mark in either the Support or Refute box. Justify your response using the law of conservation of charge.

Support Refute

Multiple choice

C5. Compared with charging by conduction using the same positive rod, how does induction differ?

Constructed response

C6. The student repeats the procedure but holds the positive rod much closer to the sphere while it is grounded. Predict how the sphere’s final charge will compare with the first trial, and explain your prediction.

Negative Induction →