electricity 2:Kirchhoff’s law, circuits, potential dividers, sensing circuits, emf, internal resistance

What is a kilowatt hour? How do you turn it into energy

Energy transferred when an appliance of power 1 kW operates for a time of one hour

(1×10³)(3600)=3.6 ×10^6 joules

What is Kirchhoff’s first law in state the equation?

Algebraic some of current flowing into a junction is equal to 0 (Conservation of charge)

I1=I2+I3

What is Kirchhoff’s second law And its equation

In any close loop, the sum of EMF is equal to the sum of potential different drops in a loop (must contain a supply)(conservation of Energy)

Sum emf= sum of p.d

What is the definition for electromotive force and this equation?

The electrical energy per unit charge provided by supply

=W/Q

What is the definition of potential difference?

What done or energy transferred per unit charged between 2 points

V=IR or V=W/Q

Series circuit summary

Current is the same for each component

Total potential difference equals the sum of potential difference across each component (shared)

Second law conservation of energy total resistance equals the sum of resistance across each component

Total resistance is always greater than resistance of individual components therefore lower current drawn

Parallel circuit summary

Total current equals the sum of current through each branch (shared)

Potential difference is the same across each branch (same)

First law conservation of charge

1/ RT = 1/ resistance 1 + 1/ resistance 2

Total resistance is always less than resistance of individual branch therefore more current drawn

In connecting cells in series, what are the characteristics for current and total emf

Current is the same

Total EMF for equal the sum of p.d

In connecting cells in parallel, what are the characteristics for current and total emf

The current will equal the total current/number of cells

The total EMF will equal the same emf in one cell

What is a potential divider and what does it do to the input and output potential difference?

Consist of two or more resistance in the series circuit connected to a source of potential difference

Input PD is shared/split by the resistors

Output PD is then measured across one of the resistors

What can potential dividers be used for in a circuit?

Temperature, volume, dimmer, speed control

Position such as gates, valves or robots

What is the equation for potential divider?

Vout=R2/Rt x Vin

Explain what a sensor circuit is, the graph and its general characteristics

Sensor circuits Detective light usually

For the graph light intensity as the x axis and resistance is the Y axis

More charge carriers delocalise therefore as light increases, resistance decreases

Since the Total resistance Decreases, the current will increase

LDR Has a lower share of input potential difference therefore the variable resistor has a higher share which also means a higher output PD

What is internal resistance?

Property of the materials From which a cell is made

Loss of potential difference per unit current, when current passes through the source due to resistance of the source itself

What is terminal potential difference?

Electrical entry per unit charge delivered by the source to the external circuit

How do you calculate the EMF in a close circuit and in an open circuit?

In a close circuit, EMF = terminal PD +’lost volts’ Due to the internal resistance

E=V+v or I(R+r)

Open circuit since there’s no current, the EMF will equal the terminal pd

E=V or IR

For an I-V graph, What is the gradient equation using the EMF equation?

The grading is constantly decreasing

E=V+v

E=V+Ir

V=-rI+E

Well, Y = V, M = -R, x= I, c=E

So the gradient is negative resistance and the Y intercept is the EMF