Electromagnetism: Circuits / Electromagnetic Radiation

Question 1

What happens when you charge an RC circuit with a capacitor?

Answer 1

Current will flow onto the capacitor, potential difference will increase

Question 2

What happens when you discharge an RC circuit with a capacitor?

Answer 2

The current flows off of the capacitor, potential difference decreases

Question 3

What is the time taken for a capacitor to charge dependent on?

Answer 3

The resistance of the resistor and capacitance of the capacitor

Question 4

What affect does increasing the resistance have on charging on discharging time?

Answer 4

It increases because less current flows at the start of the process.

Question 5

What affect does increasing the capacitance have on charging on discharging time?

Answer 5

It increases as more charge is stored on the capacitor/

Question 6

What happens to charging and discharging time when you increase the supply voltage?

Answer 6

It increases as it will take longer time for capacitor to reach higher voltage.

Question 7

What is the time constant when a capacitor is charging?

Answer 7

The time taken to increase the charge stored to 63% of the difference between initial and full charge.

Question 8

What is the time constant when a capacitor is discharging?

Answer 8

The time taken for the capacitor to discharge to 37% of its initial charge.

Question 9

In an RC circuit, when can an uncharged capacitor be considered to be fully charged?

Answer 9

After a time approximately equal to 5t. (5 times the time constant)

Question 10

What does a large time constant mean?

Answer 10

That a capacitor will charge or discharge slowly.

Question 11

Draw the diagram for Capacitors in AC Circuits

Answer 11

Remember:

• Multimeter set to ac current
• Resistor with multimeter set to ac voltage around it
• Signal generator

Question 12

What is the results of plotting a graph of current vs frequency? (Capacitor in AC circuit)

Answer 12

A straight line from Y-axis

:. Shows that current in resistor remains constant with frequency

Question 13

When a resistor is replaced with a capacitor and the experiment is repeated, what does the graph now look like? (Current vs Frequency)

Answer 13

Diagonal line from origin

Question 14

What is Capacitive reactance, Xc?

Answer 14

The opposite of a capacitor to changing current

Question 15

How do you find Capacitance from the capacitive reactance equation?

Answer 15

C = 1/

2(pi) f Xc

Question 16

When does electromagnetic induction take place?

Answer 16

When a moving magnetic field cuts a conductor to create an e.m.f across it

Question 17

What does the magnitude of the e.m.f depend on?

SLS

Answer 17

• Strength of the magnetic field
• Length of wire cutting the magnetic field
• Speed of movement

:. Greater they are, the greater induced e.m.f

Question 18

What happens if the conductor moves parallel with the magnetic field or is stationary? (Inductors in DC circuits)

Answer 18

There will be no e.m.f provided

Question 19

What does an inductor consist of?

Answer 19

coil of wire often wrapped around an iron core, which increases its effectiveness.

Question 20

What does Lenz’s Law state?

Answer 20

The induced e.m.f always opposes the change in current which causes it.

Question 21

What is the inductance, L, of an inductor?

Answer 21

• 1 H when e.m.f of one colt is induced across ends of inductor
• current in inductor changed at 1A per second

Question 22

Where is energy stored around in the magnetic field?

Answer 22

Around a current-carrying inductor.

Question 23

What is inductance, L, measured in?

Answer 23

Henries (H)

Question 24

What happens when an inductor is suddenly turned off?

Answer 24

The magnetic field rapidly collapses, producing a large back EMF

The large back EMF can create a spark across the open contacts of the switch.

Question 25

Sketch a circuit for an Inductor in AC circuits

Answer 25

Remember:

• Signal generator (• ~ •)
• Voltmeter around signal generator
• Iron-cored inductor
• Resistor next to inductor
• Ammeter

Question 26

What does a graph of current vs 1/frequency give?

Answer 26

A diagonal line from origin

Question 27

What is inductive reactance?

Answer 27

The opposition of an inductor to changing current.

Question 28

How are magnetism and electricity mutually related?

Answer 28

• changing magnetic field is able to generate an electric field
• changing electric field is able to generate a magnetic field.

Question 29

How is the electromagnetic wave formed?

Answer 29

When an electric field combines with a magnetic field.