Circuits

Question 1

What is the relationship between current, voltage and resistance?

(Symbol and word equation)

Answer 1

• V = IR
• Voltage(Volts) = Current(Amps) x Resistance(Ohms)

Question 2

What is the effect on current in a circuit when you change resistance?

Answer 2

When resistance goes up, current goes down and vice versa

(I = V/R)

Question 3

What is the relationship between current, charge and time?

(Symbol and word equation)

Answer 3

• I = Q/T
• Current(Amps) = Charge(Coulombs)/Time(Seconds)

Question 4

What is current defined as?

Answer 4

The rate of flow of charge

(because of the equation I = Q/T)

Question 5

What is the relationship between voltage, energy and charge?

(Symbol and word equation)

Answer 5

• V = E/Q
• Voltage(Volts) = Energy Tranferred(Joules)/Charge(Coulombs)

Question 6

What is voltage/potential difference defined as?

Answer 6

• Energy transferred per unit charge
• 1V = 1J/C

(because of the equation V = E/Q)

So it is the amount of energy tranferred by the charge carriers between two points in a cuircuit

Question 7

In solid metallic conductor, what is current a flow of?

Answer 7

Negatively charged electrons

Question 8

How does current work in a series circuit?

Answer 8

It is the same at all points in the circuit

Question 9

What happens to current in a series circuit when you increase the voltage?

Answer 9

Current increases

(Because of I = V/R)

Question 10

What happens to current in a series circuit when you increase the number of components?

Answer 10

Current decreases

Because resistance increases, and when resistance increases, current goes down (I = V/R)

Question 11

How does current work in a parallel circuit?

Answer 11

• The total amount of current in a circuit (dictated by the amount of voltage supplied by the battery and the total resistance) will split between each branch relative to the resistance of the branch
• The greater the resistance of that branch, the smaller the current and vice versa (I = V/R)

Question 12

Why is current conserved at a junction? (The same amount of current flows into it that flows out of it)

Answer 12

The charge is conserved (no charge has been lost or gained)

(I = Q/T)

Question 13

How does voltage work in a series circuit?

Answer 13

• The total voltage supplied by the battery/cell is split between all the components in the circuit, relative to their resistance
• So a component with higher resistance will have higher voltage (V = IR)

Question 14

How does voltage work in a parallel circuit?

Answer 14

The voltage across each branch will all be exactly the same, and will be equal to the voltage supplied by the cell/battery

Question 15

What are the advantages of using a series circuit?

Answer 15

• All of the components can be controlled by a single switch
• It is less complex and fewer wires are required

Question 16

What are the disadvantages of using a series circuit?

Answer 16

• The components cannot be controlled seperately
• If one component breaks, they all breaks

Question 17

What are the advantages of using a parallel circuit?

Answer 17

• The components can be individually controlled with their own switches
• If one component breaks, the rest of the circuit can continue to function

Question 18

What are the disadvantages of using a parallel circuit?

Answer 18

• It is more complicated and more wires are required
• All components have the same voltage, so it is difficult to control the individual voltages of each component

In summary, certain things are better suited for series circuits and some things are better with parallel
l circuits

Question 19

How does current vary with voltage across a fixed resistor or wire and what would the IV graph look like?

Answer 19

• As voltage increases, current increases, and this relationship is directly proportional
• The graph would be a straight line increasing linearly and through the origin

Question 20

How does current vary with voltage across a filament bulb and what would the IV graph look like?

Answer 20

• As voltage increases, the current increases but at an increasingly slow rate and it will eventually stop, so it is a non linear relationship
• This is because as voltage increases in a filament bulb, the temperature increases which increases the resistance, meaning current will not increase as much
• The graph will be a curve, with current going up fast at the start and then slowing down

Temperature increases resistance because it causes the positive and negative ions in the lattice of the metal in the wire to vibrate more, making it harder for electrons to pass through

Question 21

What is a diode and how does it work?

Answer 21

• A diode is a device which allows current to flow in one direction only
• It does this by having a very high resistance in the reverse direction, meaning no current can pass through (reverse bias)

Question 22

How does current vary with voltage across a diode and what would the IV graph look like?

Answer 22

• With negative voltages there will be no current as resistance is infinitely high
• There will be a turn on voltage where current goes sharply up

Question 23

What components do you need to investigate the relationship between current and voltage?

Answer 23

Make a series circuit with:

• An ammeter
• A voltmeter across the component in question
• A variable resistor
• A power source

Question 24

What is an ohmic conductor?

Answer 24

A component where voltage and current increase directly proportionally

Question 25

What is an LED?

Answer 25

A light emitting diode, meaning it will only emit light if current is flowing through it in one direction

Question 26

How can lamps and LEDS be used to indicate the presence of current in a circuit?

Answer 26

Since they both light up when there is current in the circuit, they indicate that there is current in the circuit if they light up ## Footnote An LED, however, will only light up provided the current is flowing in the right direction

Question 27

How does the resistance of a thermistor vary with temperature?

Answer 27

As the temperature **increases**, the resistance **decreases** non linearly (the decrease gets progressively slower)

Question 28

How does the resistance of a light dependant resistor vary with light intensity?

Answer 28

As light intensity **increases**, the resistance **decreases** non linearly (the decrease gets progressively slower)

Question 29

How does resistance vary with length of wire?

Answer 29

As the length of the wire increases, the resistance increases directly proportionally