Topic 3 - Spec - Electric Circuits Flashcards Preview

Physics - Topic 3 - Electric Circuits > Topic 3 - Spec - Electric Circuits > Flashcards

Flashcards in Topic 3 - Spec - Electric Circuits Deck (35)
1
Q

Define Current.

A

Current is Rate of Flow of Charge

2
Q

What is the Current Equation?

A

I = ΔQ / Δt

3
Q

What are the Components of this equation? V = W / Q

A

V - Voltage W - Work Done (I know it as E - Energy Transferred) Q - Charge

4
Q

What is the Definition for Resistance?

A

V / I

5
Q

What is Ohms Law?

A

The current through a metal wire is directly proportional to the P.D across it (Providing the TEMPERATURE is constant)

6
Q

What are materials that obey Ohms Law called?

A

Ohmic Conductors

7
Q

The Current in a […………..] circuit is the same at all points.

A

Series

8
Q

What is unusual about the Convectional Current flow and the Electron Flow?

A

Convectional Current flows from Positive to Negative Electron Flow flows in the opposite direction to Convectional Current from Negative to Positive

9
Q

What is Kirchhoffs First Law?

A

Current flowing into a junction equals the current flowing out of the junction.

10
Q

In a […………] circuit the P.D across each branch is the same.

A

Parallel

11
Q

Derive the equation for Resistance in Series.

A

1 - We know that for Resistors in series V (total) = V1 + V2 + V3 2 - we know that V = IR so replace V with IR IR (total) = IR1 + IR2 + IR3 3 - We know that for a Series circuit the current through each resistor is the same so we cancel out the I. 4 - This leaves us with R (total) = R1 + R2 + R3

12
Q

3 important facts you GUS should know about a Series Circuit.

A

1 - The current through each resistor s series is the same 2 - The total P.D across the resistors is the sum of the P.D’s across the separate resistors so : V (total) = V1 + V2 + V3 3 - The combined resistance in the circuit is the sum of the separate resistors R (total) = R1 + R2 + R3

13
Q

Derive the Equation for Resistors in Parallel.

A

1 - We know that the current is the same for Resistors in Parallel I (total) = I1 + I2 + I3 2 - We know that I = V/R so substitute this into the equation V/R (total) = V/R1 + V/R2 + V/R3 3 - Now divide each term by V This gives us 1/R (total) = 1/R1 + 1/R2 + 1/R3

14
Q

Define the Power of a Device.

A

Rate at which a device transfers energy

15
Q

What is the equation or Power which has Current in it?

A

P = IV

16
Q

How do we derive these equations? P = V²/R P = I²R

A

By using P = IV and combining Ohm’s Law V = IR

17
Q

What are the equations made from P = IV and V = IR

A

P = V²/R P = I²R

18
Q

What is the Total Electrical Energy Equation?

A

W = VIt

19
Q

What are the different variations of the Total Electrical Energy Equatoin, W = IVt ?

A

W = (V²/R) t W = I²Rt

20
Q

What is the IV graph for Ohmic Conductors?

A
21
Q

What is IV graph of a Filament Lamp?

A
22
Q

What is the IV graph for a Diode?

A
• The point at which the Diode allows current to pass is called the Threshold Voltage and it’s is about 0.6V in the Forward direction.
• Forward bias is the positive part of the IV graph - Reverse bias is the negative part of the IV Graph
• In the Reverse bias the resistance of the diode is very high and only allows a tiny amount of current to pass.
23
Q

What is the IV Graph for a Thermistor?

A
• This is a Negative Temperature Coefficient (NTC) resistor.
• Its shape is because as Voltage increase so does current, more current leads to an increase in temperature and therefore a decrease in resistance. So more current can flow because resistance decreases.
24
Q

What is the Resistivity Equation?

A

R = ρl/A

Rearranged to give

ρ = RA/l

ρ = Resistivity ( Ωm)

R = Resistance ( Ω)

A = Area (m*2)

l = Length (m)

25
Q

What is the Core Practical to find the Resistivity of a Wire?

A

1 - Find the cross sectional area of the wire, using a micrometer

2 - Clamp the wire to a ruler and connect the wire to the rest of the circuit

3 - Attach the flying lead to the test wire - Has a crocadile clip at the end so the length of wire in the circuit can be changed.

4 - Record the length of the test wire connected in the circuit, record the voltmeter and ammeter readings

5 - Use the readings to calculate the resistance in the wire R = V/I

6 - Repeat test in all sort of length ranges

7 - Plot a graph of Resistance against length and draw a line of best fit, the gradient is equal to R/I = ρ/A so get the resistivity times it by the Area.

8 - Remeber to keep the wire at a constant temperature.

8 -

26
Q

What is the Current equation with Drift Velocity in it?

A

I = nqvA

I = Current (A)

n = Number of Charge Carriers (m*-3)

q = Charge on each Carrier (C)

v = Mean drift Velocity (ms-1)

A = Cross-sectional Area (m*2)

27
Q

What is the Charge on each Electron?

A

-1.6x10*-19

28
Q

What are the Potential Divider Equations?

A

V (out) / V (in) = R1 / R1 + R2

or

V (out) = V (in) x R1/R1 + R2

29
Q

Potential Divider Circuits which include Light Dependent Resistors (LDR) and Thermistors.

A
• With a Thermistor its resistance rises as it COOLS, this means V (out) increases
• For an LDR as light intensity increases the resistance decreases.
30
Q

Define E.M.F.

A

Is the electrical energy supplied per coulomb of charge.

ℰ = W/Q

31
Q

What is meant by Internal Resistance?

A

Is the energy that is wasted or ‘lost’ as the coulombs move against the resistance of the cell itself

32
Q

What is the Difference between E.M.F and Terminal P.D?

A

E.M.F measures how much charge is gained

Terminal P.D is the voltage around the whole circuit taking into account Internal Resistance

33
Q

Determine the E.M.F and Internal Resistance of an electrical cell CORE PRACTICAL

A
• Create a circuit with a cell with internal Resistance, a variable resistor, a Voltmeter and Ammeter.
• Vary the current in the circuit by changing the load resistance, measure the P.D
• Plot the results on a V I graph
• Use the equation Є = V + Ir and rearrange the equation to give V = -rI + Є
• Since Є and r are constants we can use the straight line equation y = mx + c
• So the intercept on the VERTICAL AXIS is Є
34
Q

Explain the effect of temperature on resistance.

A
• Metals contain large numbers of free electrons and as these free electrons love through the lattice they collide with the vibrating metal ions.
• This causes the metals temperature to increase, leading to the ions to vibrate faster with greater amplitude.
• This increases the amount of collisions which oppose the flow of electrons and causes the metals resistance to increase.
35
Q
A