Current, potential difference and resistance (2.1) (R)

Question 1

What is the symbol for a switch (open and closed)?

Answer 1

Question 2

What is the symbol for a cell and battery?

Answer 2

Question 3

What is the symbol for a diode?

Answer 3

Question 4

What is the symbol for a resistor?

Answer 4

Question 5

What is the symbol for a variable resistor?

Answer 5

Question 6

What is the symbol for a LED?

Answer 6

Question 7

What is the symbol for a lamp?

Answer 7

Question 8

What is the symbol for a fuse?

Answer 8

Question 9

What is the symbol for a voltmeter?

Answer 9

Question 10

What is the symbol for an ammeter?

Answer 10

Question 11

What is the symbol for a thermistor?

Answer 11

Question 12

What is the symbol for an LDR?

Answer 12

Question 13

What must the circuit include for electrical charge to flow through a closed circuit?

Answer 13

a source of potential difference

Question 14

What is electrical current?

Answer 14

a flow of electrical charge

Question 15

What is the size of the electric current?

Answer 15

the rate of flow of electrical charge

Question 16

A current has the (…) value at (…) point in a (…) closed loop

Answer 16

same

any

single

current is not used up

Question 17

2 things

What does the current through a component depend on?

Answer 17

Both the resistance of the component and the potential difference across the component

Question 18

The greater the resistance of the component the (…) the current for a given potential difference (pd) across the component.

Answer 18

smaller

Question 19

Describe a method to investigate how changing the length of the wire affects its resistance.

Answer 19

1. Connect the circuit as shown in the diagram attached.
2. Connect the crocodile clips to the resistance wire, 100 centimetres (cm) apart.
3. Record the reading on the ammeter** and on the **voltmeter.
4. Move one of the crocodile clips closer until they are 90 cm apart.
5. Record the new readings on the ammeter and the voltmeter.
6. Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm.
7. Use the results to calculate the resistance of each length of wire by using R = V/I, where R is resistance, V is voltage and I is current.
8. Plot a graph of resistance against length for the resistance wire.

Question 20

How does the value of resistance depend on the current in different resistors?

Answer 20

In some resistors is the value of the resistance constant, whereas in others it can change as the current changes?

some are fixed resistors and some are variable resistors

Question 21

What is Ohm’s law?

Answer 21

that the voltage across a conductor is directly proportional to the current flowing through it

Question 22

Describe the current through an ohmic (fixed) conductor

Answer 22

The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes.

obey ohm’s law

Question 23

How would you describe the resistance of components such as lamps, diodes, thermistors and LDRs?

Answer 23

not constant

it changes with the current through the component

Question 24

Describe the correlation between the resistance through a filament lamp and temperature

Answer 24

The resistance of a filament lamp increases as the temperature of the filament increases.

Question 25

Describe the current through a diode

Answer 25

The current through a diode flows in one direction only

Question 26

Describe the resistance of a diode in the reverse direction

Answer 26

The diode has a very high resistance in the reverse direction *up until a particular voltage, the current will remain 0, and then quickly increase at the value*

Question 27

What component does this graph represent the resistance of?

Answer 27

ohmic (fixed) resistor

Question 28

What component does this graph represent the resistance of?

Answer 28

filament lamp

Question 29

What component does this graph represent the resistance of?

Answer 29

diode

Question 30

The resistance of a thermistor (…) as the temperature increases

Answer 30

decreases

Question 31

What is the application of thermistors?

Answer 31

thermostats *(and other temperature sensors)*

Question 32

The resistance of an LDR (…) as light intensity increases

Answer 32

decreases *used to detect light levels*

Question 33

What is an application of LDRs?

Answer 33

switching lights on when it gets dark *how street lamps work*

Question 34

Draw a circuit diagram with a cell, ammeter, voltmeter, and variable resistor

Answer 34

Question 35

Describe a method to investigate the relationship between current and potential difference for a resistor, bulb and diode

Answer 35

1. Connect the circuit as shown 2. Ensure that the power supply is set to zero at the start. 3. Record the reading on the **_voltmeter**_ and _**ammeter_**. 4. Use the **_variable resistor_** to alter the potential difference. 5. Record the new readings on the voltmeter and ammeter. 6. Repeat steps three to four, each time increasing the potential difference slightly. 7. Reverse the power supply connections and repeat steps two to six. 8. Plot a graph of current against potential difference for each **_component_**. 9. Repeat the experiment but replace the **_fixed resistor_** with a bulb and then diode

Question 36

What is the supply of circuits powered by batteries or cells

Answer 36

dc

Question 37

Draw a graph for a thermisistor

Answer 37

*low heat on left of x axis, high heat on right*

Question 38

Draw a graph for an LDR

Answer 38

*dark on left of x axis, bright on right*

Question 39

What are conventional currents?

Answer 39

Current flows from the negative end of the cell to the positive end. However scientists always draw the current in the opposite direction (due to prior beliefs). We call this conventional currents.