23.4- DIELECTRICS

Question 1

How can the charge stored on the plates of a capacitor be increased?

Answer 1

by inserting a dielectric between the plates

Question 2

What are dielectrics?

Answer 2

electrically insulating materials that increase ability of parallel-plate capacitor to store charge when dielectric placed between plates of capacitor

Question 3

What are examples of dielectrics? (2)

Answer 3

polythene

waxed paper

Question 4

What happens when a dielectric is placed between two oppositely charged parallel plates connected to a battery?

Answer 4

each molecule of dielectric becomes polarised

Question 5

What does it mean for each molecule of the dielectric becoming polarised when it is placed between two oppositely charged parallel plates connected to a battery?

Answer 5

its electrons pulled slightly towards the positive plate

Question 6

What happens to the surface of the dielectric facing the positive plate when a dielectric is placed between two oppositely charged parallel plates connected to a battery and what happens to the other surface?

Answer 6

gains negative charge a expense of other side of dielectric that faces negative plate

other surface of dielectric loses negative charge, so some positive charge left on its surface

Question 7

What are molecules like in some dielectric substances?

Answer 7

molecules already polarised but they lie in random directions

Question 8

When do the polar molecules of a dielectric turn?

Answer 8

when dielectric placed between charged plates

Question 9

Why do the polar molecules of a dielectric turn when it’s placed between charged plates?

Answer 9

as their electrons attracted slightly to positive plate

Question 10

What is the effect like with non-polar molecules of a dielectric in comparison to polar molecules?

Answer 10

same

surface of dielectric near positive plate gains negative charge, and surface gains positive charge

Question 11

Why is there more charge stored on the plates?

Answer 11

positive side of dielectric attracts more electrons from battery onto negative plate

negative side of dielectric pushes electrons back to battery from positive plate

Question 12

What is the effect of a dielectric to do?

Answer 12

increase charge stored in capacitor for any given pd across capacitor terminals

increase capacitance of capacitor

Question 13

For a fixed pd across a parallel-plate capacitor with an empty space between its plate, what happens to charge when a dielectric is inserted between the plates?

Answer 13

charge stored increased

Question 14

What is the relative permittivity of a dielectric substance?

Answer 14

ratio of charge stored with dielectric to charge stored without dielectric

Question 15

What is the relative permittivity of a substance also called?

Answer 15

its dielectric constant

Question 16

What is the equation for capacitance for a parallel-plate capacitor with dielectric filling the space between the plates?

Answer 16

C = Aε0εr / d

εr- relative permittivity
A- surface area of each plate
d- spacing between plates

Question 17

How can a large capacitance be achieved? (using C = Aε0εr / d)

Answer 17

making area A as large as possible

making plate spacing d as small as possible

filling the space between the plates with a dielectric which has a relative permittivity as large as possible

Question 18

What do most capacitors consist of?

Answer 18

two strips of aluminium foil separated by layer of dielectric