P3.2 Simple Circuits

Question 1

What happens to resistance of thermistor as temperature increases

Answer 1

Thermistor’s resistance decreases
OPPOSITE TO NORMAL RESISTORS

Question 2

Switch circuit symbol

Answer 2

Open
-o o-
. \

Closed
-o—o-

Question 3

Circuit symbol for a lamp

Answer 3

—⨂—

Question 4

Circuit symbol for a fuse

Answer 4

⏛

Question 5

Voltmeter circuit symbol

Answer 5

—Ⓥ—

Question 6

Circuit symbol for an ammeter

Answer 6

—Ⓐ—

Question 7

Diode

Answer 7

. ___
—(▷I)—
. ‾‾‾‾
current only flows in one direction.
Resistance is very high in the other direction, preventing current flow.

Question 8

Resistor circuit symbol

Answer 8

—▭—

Question 9

Thermistor circuit diagram

Answer 9

. /
—▭—
. _/

Question 10

Circuit symbol for a variable resistor

Answer 10

—↗—

Question 11

LDR

Answer 11

↘↘
. —(▭)—

Used in street lamps or night lights.
When light levels become low enough, the light gains sufficient current to turn on.

Question 12

LED circuit symbol

Question 13

Series circuit

Answer 13

Same charge passes through all components,
so current through each component is same
Voltage is SPLIT

Question 14

What is a parallel circuit?

Answer 14

A circuit in which the charge is split between branches.

Question 15

What two factors does the current in a circuit depend on?

Answer 15

1. Potential Difference (V)
2. Resistance (R)

Question 16

What equation should be used to calculate potential difference if current and resistance are known? State the units for all 3 quantities.

Answer 16

V = IR
Potential Difference (V), Current (A),
Resistance (ohms)

Question 17

Ohmic Conductor and conditions required

Answer 17

Conductor for which current and potential difference are directly proportional
Resistance remains constant as current changes
Temperature must be constant

Question 18

4 components for which resistance is not constant as current changes.

Answer 18

1. Lamps
2. Diodes
3. Thermistors
   Light Dependant Resistors (LDRs)

Question 19

What happens to the resistance of a filament lamp as the temperature increases? Why?

Answer 19

Resistance increases.
• Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance.

Question 20

examples of when a thermistor may be used

Answer 20

In a thermostat to turn a heater on below a certain temperature.
2. In a freezer to turn on a cooler when the temperature becomes too high.

Question 21

State what happens to the resistance of a LDR as light intensity decreases.

Answer 21

The LDR’s resistance increases.

Question 22

What are the two ways that a component can be connected in a circuit?

Answer 22

Series (same loop)
2. Parallel (adjacent loop)

Question 23

How potential difference across components varies when connected in series and parallel

Answer 23

Series: Total PD is SPLIT between each component
Parallel: PD across each component is same

OPPOSITE FOR CURRENT

Question 24

If two resistors are connected in parallel, what can be said about their combined total resistance?

Answer 24

Their total resistance is less than the smallest of the two individual resistances.

Question 25

If two resistors are connected in series, what can be said about their total resistance?

Answer 25

Their total combined resistance is equal to the sum of the two individual resistances.

Question 26

equations for the power of a circuit. Give appropriate units.

Answer 26

P = I V
P = 1²R
Power (Watts), Current (Amperes), Potential Difference (Volts), Resistance (Ohms)

Question 27

State an equation linking energy transferred, power and time. Give appropriate units.

Answer 27

E= Pt
Energy (Joules), Power (Watts), Time (Seconds)

Question 28

Equation linking energy transferred, power and time

Answer 28

E= QV
Energy (Joules), Charge (Coulombs), Potential Difference (Volts)
Energy = power

Question 29

How should a voltmeter be connected in a circuit?

Answer 29

In parallel to the component that you are measuring the potential difference for.

Question 30

How should an ammeter be connected in a circuit?

Answer 30

In series with the branch you are measuring the current for.