1 Electrostatics and Current

Question 1

Two insulating materials are rubbed together.

They are charged by friction.

Which particle is transferred between them?

Answer 1

Electrons

Question 2

Charge does not flow easily through what sort of material?

Answer 2

insulators

eg plastic or wood

Question 3

What is the current if 7200 C passes in 1 hour ?

Answer 3

I = Q/t

time must be in seconds

1 hour = 1 x 60 x 60 = 3600 secs

I = 7200 C/ 3600 s

I = 2 A

Question 4

What is the current if 360 C passes a point in a circuit in 2 min?

Answer 4

I = Q/t

time must be in seconds

2 min = 2 x 60 = 120 seconds

I = 360 C / 120s

I = 3 A

Question 5

Name three uses of electrostatics

Answer 5

1. electrostatic smoke removal from chimneys
2. photocopier
3. inkjet printer
4. electrostatic paint sprayer
5. electrostatic crop sprayer

Question 6

Where are neutrons located in an atom?

Answer 6

in the nucleus

Question 7

If 3nC of electrons were transferred from a cloth to the surface of the rod, what is the charge on the rod?

Answer 7

• 3 nC

negative charge as the rod has gained electrons

Question 8

What happens when two negatively charge balloons hang side by side?

Answer 8

They repel because

like charges repel

Question 9

What is the current if 100 C passes in 200s ?

Answer 9

I = Q/t

I = 100 C/ 200 s

I = 0.5 A

Question 10

What does the prefix ‘nano’ stand for in 10 nC

Answer 10

nano means x 10^-9

example 10 nC = 10 x 10^-9 C

Question 11

What is the definition for current?

Answer 11

Current = the rate of flow of charge

I = Q/t

Question 12

Only electrons are transferred when objects are charged by friction. Why?

Answer 12

Electrons are located in the outer shells of an atom so are easily removed.

But protons are located in the nucleus at the centre of the atom so cannot be removed easily.

Question 13

If 5 mA flows for 10 minutes, how much charge flows?

Answer 13

Q = I x t

time must be in seconds

t = 10 x 60 = 600 seconds

Current must be in amps

I = 5 mA = 5 x 10^-3 A

Q = 5 x 10^-3 x 600 = 3C

Question 14

A negatively charged polythene rod is scraped across a gold leaf electroscope. The gold leaf rises.

Look at the diagram to explain why?

What would you observe if the same thing was done with a postive acetate rod?

Answer 14

The gold foil rises as it is repelled from the central post as like charges repel.

Same would happen for both acetate and polythene but with opposite charges.

Question 15

What is the symbol for an ammeter and how is it connected in the circuit?

Answer 15

An ammeter is connected in series

Question 16

A acetate rod is charged by friction? What charge does it gain?

Answer 16

Acetate loses electrons to the cloth to become positively charged

Question 17

What does the prefix ‘micro’ stand for in 100 uA

Answer 17

micro x 10^-6

example : 100 uC = 100 x 10^-6 C

Question 18

What does the prefix milli stand for in 65 mA

Answer 18

milli is x 10^-3

example: 65 mC = 65 x 10^-3 C

Question 19

What would happen if two negatively charge balloons were hung side by side?

Answer 19

They would repel because

like charges repel

Question 20

If 100 A flows for 10 s, how much charge passes?

Answer 20

Q= I x t

Q = 100 A x 10 s = 1000 C

Question 21

What is the current if 10 nC passes in 5 s ?

Answer 21

I = Q/t

first convert 10nC to coulombs

10nC = 10 x 10^-9 C

I = 10 x 10^-9/ 5

I = 2 x 10^-9 A

Question 22

What equation links charge, current and time?

Answer 22

Charge = current x time

Q=It

or

Current = charge / time

I=Q/t

Question 23

What would happen if two negatively charge balloons were hung side by side?

Answer 23

The would repel because

like charges repel

Question 24

Where are protons located in an atom?

Answer 24

the nucleus

Question 25

What sort of material will allow charge to flow through it?

Answer 25

conductors such as a metal

Question 26

What is the relative charge of an electron?

Answer 26

-1

Question 27

What charge would a rod adopt if 5nC of electrons were transferred from its surface to a cloth?

Answer 27

+ 5 nC

Question 28

What would happen if two positively charge balloons were hung side by side?

Answer 28

The would repel because like charges repel

Question 29

How can a charged object be discharged?

Answer 29

Earth it. Connect a wire conductor from the object to a stake in the ground.

Question 30

What is the relative charge of a proton?

Answer 30

+1

Question 31

A polythene rod is rubbed with a cloth. What happens?

Answer 31

Electrons transfer from the cloth to the rod.

The polythene rod becomes negatively charged

The cloth becomes postively charged

Question 32

What is the relative charge of neutron?

Answer 32

0

Question 33

An acetate rod is rubbed with a cloth. What happens?

Answer 33

Electrons transfer from the rod to the cloth.

The acetate rod becomes positively charged

The cloth becomes negatively charged

Question 34

If 4 A flows for 2 minutes, how much charge flows?

Answer 34

Q = I x t

Q = 4 A x (2 x 60s ) = 480C

time must always be converted into seconds

Question 35

Where are electrons located in an atom?

Answer 35

shells orbiting the nucleus

Question 36

Name three dangers of electrostatic charge

Answer 36

1. Refueling cars or aircraft
2. explosion of dust or fine powder in industry
3. Lightning from charge build up in clouds
4. Spark in operating theatre- explosion of oxygen

Question 37

What can we use to measure charge?

Answer 37

A nanocoulombmeter

Question 38

How can we reduce the electrostatic force acting on the objects below?

Answer 38

Move the objects further apart OR decrease their charge.

Question 39

What would happen if a negatively charged balloon and a positively charge balloon were hung side by side?

Answer 39

They attract because

unlike charges repel