Electrical Circuits

Question 1

diode circuit symbol

Answer 1

playbutton in a circle with a line through it

Question 2

resistor circuit symbol

Answer 2

rectangle

Question 3

variable resistor circuit symbol

Answer 3

rectangle with an arrow through it pointing right

Question 4

thermistor circuit symbol

Answer 4

rectangle with a diagonal line pointing right with a tail at the bottom left

Question 5

fuse circuit symbol

Answer 5

rectangle with a line through it

Question 6

battery circuit symbol

Answer 6

two cells, longest line first, joined by dotted line

Question 7

equation for charge

Answer 7

• charge(C)= current(A)x time(s)
  *Q=It

Question 8

what is current caused by? explain why

Answer 8

• current is caused by a source of potential difference
• because electrons are removed from atoms (being left as +ions), the potential difference between the two causes the electrons to be attracted back, producing a flow of charge, producing current electricity
• it is the same at any point in a series circuit

Question 9

what is potential difference?

Answer 9

a measure of energy per unit of charge transferred between two points in a circuit

Question 10

what happens to the current for a given potential difference across the component in series when the resistance is increased?

Answer 10

the current for a given potenetial difference across the component decreases because adding resistors in series decrease the total current through the circuit because it becomes harder for electricity to move through the component and current is the same at any point in a series circuit

Question 11

equation for potential difference

Answer 11

• potential difference(V)= current(A) x resistance(Ω)
  *V=IR

Question 12

what is an ohmic conductor

Answer 12

a conductor that obeys ohm’s law (that current flowing through a resistor is proportional to potential difference and inversely proportional to resistance, provided the temperature remains constant)

Question 13

what would an IV graph of an ohmic conductor look like, why and explain it’s resistance

Answer 13

• a straight diagonal line from left to right, passing through (0,0)
• because the current through an ohmic conductor is directly proportional to potential difference, so you get a straight line
• it is a resistor

Question 14

what would an IV graph of a lamp look like, why and explain it’s resistance

Answer 14

• a diagonal but curved (slightly S shaped) line from left to right, going through (0,0)
• when the current increases, the temperature of the filament increases, so the resistance increases
• this means that less current can flow per unit of potential difference, so the graph gets shallower- hence the curve

Question 15

what would an IV graph of a diode look like, why and explain it’s resistance

Answer 15

• line is flat against x axis (V axis) until a bit after it hits the y axis (I axis), it curves up
• because current only flows through diodes in one direction
• the diode has a very high resistance in the other direction

Question 16

what would a graph of an LDR look like, why and explain it’s resistance

Answer 16

• y axis= resistance, x axis= light intensity
• curves down from e.g. (1,10) to (10,1)
• because it is a resistor that is dependent on light intensity
• in bright light, resistance falls and resistance is highest in darkness
• e.g. automatic night lights, outdoor lights, burglae detectors

Question 17

what would a graph of a thermistor look like, why and explain it’s resistance

Answer 17

• y axis= resistance, x axis= temperature
• curves down from e.g. (1,10) to (10,1)
• because a thermistor is a resistor that depends on temperature
• resistance decreases as temperature increases so in hot conditions, resistance drops and in cold conditions, the resistance goes up
• temperature detectors e.g. car engine temperature sensor, electronic thermostat

Question 18

resistance in series

Answer 18

Rtotal= R1+R2

Question 19

components in series have the same what? give an equation and explanation

Answer 19

• current
• because there is only a single pathway for the charge to flow
• I1=I2=I3

Question 20

components in parallel have the same what? give an equation

Answer 20

• potential difference
• V1=V2=V3

Question 21

why does adding resistors in series increase total resistance but adding resistors in parallel decrease the total resistance?

Answer 21

• because in series the current has to flow through each resistor in turn so adding additional resistors adds to the resistance, making it harder for the current to flow through
• in parallel, the current has a choice of paths and only has to pass along one branch of the circuit so does not pass through each resistor