2 Electricity

Question 1

What are the circuit symbols?

Answer 1

Click me for flashcards!

Question 2

What is needed for charge to flow? (2)

Answer 2

1) The circuit must be closed (no open switches).
2) There must be a source of potential difference (battery/cell).

Question 3

What is current?

Answer 3

The rate of flow of electrical charge.

Question 4

What is the equation for charge flow?
(Provide the quantities, the unit’s symbols, and the quantities’ symbols.)

Answer 4

Charge (C) = current (A) × time (s)
Q = It

Question 5

What happens to current in a single closed loop (e.g. series circuit)?

Answer 5

The current has the same value at any point.

Question 6

What factors affect the current flowing through a component? (2)

Answer 6

1) The resistance (R) of the component.
2) The potential difference (V) across the component.

Question 7

Explain the relationship between the resistance, current, and potential difference.

Answer 7

The larger the resistance of a component, the smaller the current for a given potential difference across the component.

Question 8

What is the equation for voltage and current? (2)
(Provide the quantities, the unit’s symbols, and the quantities’ symbols.)

Answer 8

Voltage (V) = current (A) × resistance (Ω)
V = IR

Current (A) = voltage (V) ÷ resistance (Ω)
I = V/R

Question 9

What is an ohmic conductor? (3)

Answer 9

• A kind of resistor (conductor) in which the resistance is constant, so, the resistance stays the same as the current changes.
• The current is directly proportional to the potential difference.

Question 10

What condition is needed for the resistance to remain constant?

Answer 10

A constant temperature.

Question 11

How is the relationship of the current and potential difference for an ohmic conductor (fixed resistor) presented in a graph? (3)

Answer 11

[Click me to see graph!]
It is a linear graph, with the current against the potential difference, with a constant resistance.

Question 12

What happens when the resistance is not constant? How does this affect the current and potential difference? (2)

Answer 12

• The resistance will change depending on the current flowing through the component.
• The current is not directly proportional to the potential difference.

Question 13

What components do not have a constant resistance as the current changes? (4)

Answer 13

• Lamp
• Diode
• Thermistor
• LDR

Question 14

What happens to the resistance of a filament lamp? (1) Why? (3)

Answer 14

1) The resistance of the lamp increases as the temperature of the filament increases.

1. As the temperature of the filament increases, the atoms in the lamp vibrate more.
2. The electrons in the current collide more with the atoms in the filament.
3. so more energy is needed to push the current through the filament.

Question 15

How is the relationship of the current and potential difference for a filament lamp presented in a graph?

Answer 15

Click here to see graph!

Question 16

What happens to the current flow of a diode due to resistance? (2)

Answer 16

1) The current only flows in one direction as the resistance of the diode is low (and the diode allows this).
2) Resistance is very high in the other direction, preventing current flow.

Question 17

How is the relationship of the current and potential difference for a diode presented in a graph?

Answer 17

Click me to see graph!

Question 18

Explain the relationship between resistance and current (see if you can explain why). (5)

Answer 18

As the resistance increases, current decreases.

1. As current increases, electrons (charge) gain more energy.
2. When electrons flow through a resistor, they collide with the atoms in the resistor,
3. which transfers energy to the atoms, causing them to vibrate more,
4. making it more difficult for electrons to flow through the resistor.

Question 19

Explain the relationship between resistance and temperature (see if you can explain in why). (5)

Answer 19

As the temperature increases, the resistance increases.

1. As temperature increases, electrons (charge) gain more energy.
2. When electrons flow through a resistor, they collide with the atoms in the resistor,
3. which transfers energy to the atoms, causing them to vibrate more,
4. making it more difficult for electrons to flow through the resistor.

Question 20

What happens to the resistance of a thermistor due to temperature? (2)

Answer 20

As the temperature increases, the resistance decreases.

Question 21

Where are thermistors normally used? (2)

Answer 21

• Thermostats
• Temperature detectors (e.g. replacement fuse)

Question 22

Explain the relationship between resistance and wire length (see if you can explain in why). (3)

Answer 22

The greater the length, the more resistance and the lower the current.

1. Electrons have to make their way through more resistor atoms,
2. so it is harder to flow through than using a shorter wire.

Question 23

What happens to the resistance in a LDR due to light intensity? (2)

Answer 23

The greater the light intensity, the lower the resistance, so, the resistance is greater when it is dark.

Question 24

Where are LDRs used?

Answer 24

• Automatic night lights (e.g. streetlights)