Current electricity

Question 1

What happens when two electrically insulating materials are rubbed together?
The way in which the electrons are transferred depends on what?

Answer 1

When two electrically insulating materials are rubbed together, electrons are rubbed off one material and deposited on the other.
They way in which the electrons are transferred depends on the particular materials.

Question 2

When electrons are transferred between materials, what charge does the object that gained electrons have?
What charge does the material that has lost electrons have?
What is this process called?

Answer 2

The material that has gained electrons becomes negatively charged because electrons have a negative charge.
The material that has lost electrons has a positive charge.
This process is called charging by friction.

Question 3

How does the charge of objects affect their attraction to each other?
How does the distance between the objects affect the force between them?

Answer 3

Objects that have opposite electric charges are attracted to each other. Objects that have have the same electric charges repel each other.
The greater the distance between the objects, the weaker the force between them.

Question 4

How is the current in an electrical circuit calculated?

Answer 4

I = Q/t
I is the current in amperes, A
Q is the charge in coulombs, C
t is the time in seconds, s

Question 5

How is the current through a component measured?

How are ammeters connected to the component?

Answer 5

The current through a component is measured with an ammeter, ammeters are always placed in series with the component.

Question 6

How is the potential difference across a component measured?
How are voltmeters connected to the component?
What is the unit of potential difference?

Answer 6

The potential difference across a component is measured using a voltmeter, which are placed in parallel with the component.
The unit of potential difference is the volt, V.

Question 7

What equation links potential difference, work done and charge?

Answer 7

V = W/Q
V is the potential difference in volts, V
W is the work done in joules, J
Q is the charge in coulombs, C

Question 8

What equation links potential difference and energy transferred?

Answer 8

V = E/Q

E is the energy transferred in joules, J

Question 9

What is resistance and what is the unit of resistance?

Answer 9

Resistance is the opposition to current flow and the unit of resistance is the Ohm.

Question 10

How can the resistance of a component be calculated?

Answer 10

R = V/I
R is the resistance in ohms
V is the potential difference in volts, V
I is the current in amperes, A

Question 11

What are current-potential difference graphs used to show?

Answer 11

Current-potential difference graphs are used to show how the current through a component varies with the potential difference across it.

Question 12

What is Ohm’s law?

What is any component that obeys Ohm’s law called?

Answer 12

Ohm’s law states that the current is directly proportional to the potential difference across the resistor.
Any component that obeys Ohm’s law is called an ohmic conductor.

Question 13

What will the current-potential difference graph look like for a resistor kept at a constant temperature?

Answer 13

The current-potential difference graph for a resistor kept at a constant temperature shows a straight line passing through the origin.

Question 14

What is the line on a current-potential difference graph for a filament bulb, what does this tell us about the bulb?

Answer 14

The line on a current-potential difference graph for a filament bulb is a curve, so the current is not directly proportional to the potential difference.

Question 15

How is the resistance of a filament bulb affected by the current and why is this?
What affect does reversing the potential difference to the shape of the curve?

Answer 15

The resistance of a filament bulb increases as the the current increases, this is because the resistance increases as the temperature increases.
Reversing the potential difference makes no difference to the shape of the curve.

Question 16

What can be said about the current through a diode, why is this?

Answer 16

The current through a diode flows in only one direction, because in the reverse direction the diode has a very high resistance so the current is zero.

Question 17

What happens to the resistance of a light dependent resistor (LDR) as the light falling on it gets brighter?

Answer 17

As the light falling on an LDR increases, the resistance decreases.

Question 18

What happens to the resistance of a thermistor as the temperature increases?

Answer 18

As the temperature increases, the resistance of a thermistor decreases.

Question 19

What happens to charge in a series circuit if there is a break in the circuit and why?

Why is the current through each component in a series circuit the same?

Answer 19

In a series circuit, if there is a break in the circuit, charge stops flowing because all the components are connected one after another.
The current through each component in a series circuit is the same because there is no choice of route for the charge as it flows around the circuit.

Question 20

What is the current in a series circuit dependent on?

What equation shows this?

Answer 20

The current in a series circuit is dependent on the potential difference of the supply and the total resistance of the circuit.
I = V/R

Question 21

Why does the pd across the individual components in a series circuit add up to give the pd supply?

Answer 21

As the pd of the supply is shared between all the components in the circuit.

Question 22

The resistances of the individual components of a series circuit add up to give what?
What is a components share of the supply pd dependent on?

Answer 22

The resistances of the individual components in a series circuit add up to give the total resistance of the circuit.
The bigger the resistance of a components, the bigger its share of the supply pd.

Question 23

Why is the charge in a parallel circuit still able flow in the other parts of the circuit if there is a break in the circuit?

What does this mean about the pd across each component?

Answer 23

As in a parallel circuit, each component is connected across the supply.

The pd across each component is the same, as each component is connected across the supply pd.

Question 24

Why can different amounts of charge flow through different components in a parallel circuit?

Answer 24

There are junctions in the circuit so different amounts of charge can flow through different components

Question 25

What does the current through each component in a parallel circuit depend on?
How does this affect current?

Answer 25

The current through each component in a parallel circuit depends on its resistance, the bigger the resistance of a component, the smaller the current through it.

Question 26

The current through a component in a parallel circuit can be calculated using which equation?
What is the total current through the whole circuit equal to?

Answer 26

I = V/R

The total current through the whole circuit is equal to the sum of the currents through the separate components.