Chapter 4 - Electric Circuits

Question 1

What is an ion?

Answer 1

• A charged atom

Question 2

How does an insulating material become positively charged?

Answer 2

• The material is rubbed against another material, causing loss of electrons.

Question 3

What does a material do to become negatively charged?

Answer 3

• Gain of electrons

Question 4

Define electric current.

Answer 4

• The rate of flow of charge in a circuit.

Question 5

State all of the components you might find in a circuit.

Answer 5

• Battery
• Switch
• Bulb
• Diode
• Light-Emitting Diode (LED)
• Ammeter
• Fixed Resistor
• Variable Resistor
• Fuse
• Voltmeter

Question 6

Write the equation that links current, charge flow and time taken.

Answer 6

Charge Flow (Q)   =   Current (I)      x     Time Taken(t)
 (couloumbs, C)        (amperes, A)           (seconds, s)

Question 7

What is the purpose of a fuse?

Answer 7

• To break the circuit if the current passing through is greater than an amount.

Question 8

What is the purpose of an LED?

Answer 8

• Emits light when current passes through it.

Question 9

Give the equation that links potential difference, charge and energy transferred.

Answer 9

Potential difference (V)    =      Energy Transferred (E)      /    Charge (Q)
       (Volts, V)                                      (Joules, J)                    (couloumbs, C)

Question 10

State Ohm’s Law

Answer 10

• Current through a resistor at constant temperature is directly proportional to the p.d across the resistor.

Question 11

Write the equation that links potential difference, resistance and current.

Answer 11

Resistance (R) = Potential Difference (V) / Current (I)
(ohms) (Volts, V) (amperes, A)

Question 12

Describe a current - potential difference graph of a filament lamp.

Answer 12

• Not directly proportional to the p.d
• Resistance increases as current increases
• Reversing the p.d reverse the current

Question 13

Describe a current - potential difference graph for a diode.

Answer 13

• In the forward direction, the current isn’t directly proportional to the p.d
• In the reverse, current is zero. The diodes resistance is higher than in the forwards direction.

Question 14

What happens to the resistance of a thermistor?

Answer 14

• Resistance decreases when temperature increases.

Question 15

What happens to the resistance of an LDR?

Answer 15

• Resistance decreases as light intensity increases.

Question 16

For components in series, state the circuit rules.

Answer 16

• Same current passes through each component.
• Total p.d of the power supply is shared between components.
• Total p,d of cells in series = sum of p.d of each cell.

Question 17

How do you calculate the total resistance of two (or more) components in series?

Answer 17

R = R1 + R2
total

R1 = Resistance of first component
R2 = Resistance of second component

Question 18

For components in parallel, state the circuit rules.

Answer 18

• Total current through the circuit = sum of currents through the separate branches.
• P.D across each component is the same.
• Total resistance of two (or more) components is less than resistance of resistor with the least resistance.

Question 19

How do you calculate the current through a resistor?

Answer 19

I = V/R