---

---

Electronic Components

Circuit Diagram Symbols
(from studyrocket.co.uk)

I-V Characteristics

Investigating I-V Characteristics

---

Resisitance

---

Prerequisite Materials:

Current

Potential Difference
(Care of www.gcsephysicsonline.com)

---

Resistance - defining equation - Ohm's Law:

$$V=IR$$

• where
• $V$ is the potential difference across the component in volts, $V$;
• $I$ is the current through the component in amperes, $A$;
• and
• $R$ is the resistance of the component in ohms, $\Omega$.

---

The Rearrangements

---

---

Current

Definition of Electrical Current $$I=\frac{Q}{t}$$

(AKA Conventional Current)
(from simple.wikipedia.org)

• where
• $I$ is the electrical current in amps, $A$;
• $Q$ is the charge that is moving in coulombs, $C$;
• and
• $t$ is the time taken, for the flow to occur, in seconds, $s$.

---

• Kirchhoff's Current Law, and Kirchhoff's e.m.f and p.d. Law from isaacphysics.org;
  
• See electron flow from alevelphysics.co.uk.
  

---

Questions

Electrical Charge-and Current
(Care of mmerevise.co.uk)

Circuits, Charge and Current
(Care of revisionscience.com)

Current
(Care of www.savemyexams.com)

---

Mains Electricity

Mains Electricity
(Care of mmerevise.co.uk)

Revision Questions
(Care of www.gcsescience.com)

Mains Electricity
(Care of studymind.co.uk)

---

Electrical Power

Warm-up Materials:

---

Describing Electrical Power

$$P=IV$$

• where
• $P$ is the electrical power delivered to the component, in watts, $W$;
• $I$ is the electrical current passing through the component, in amperes, $A$;
• and
• $V$ is the potential difference across the component, in volts, $V$;

---

The Rearrangements

---

Other Forms

Using Ohm's Law we can express electrical power as

---

This equation can be derived from the equation for mechanical power along with the definitions for both current and potential difference

$$P=\frac{W}{t}$$

$$I=\frac{Q}{t}\Rightarrow t=\frac{Q}{I}$$

$$V=\frac{W}{Q}\Rightarrow W=VQ$$

Combining these three ...

$$P=\frac{VQ}{Q/I}=IV$$

---

Questions:

Power
(Care of mmerevise.co.uk)

Energy and Power in Circuits
(Care of www.savemyexams.com)

---

The Charge Transport Equation

$$I=Anqv$$

• where
• $I$ is the current in amperes, $A$;
• $n$ is the number of charge carriers per unit volume, $m^{-3}$;
• $A$ is the cross-sectional area perpendicular to the current flow, $m^2$;
• $q$ is the charge on each carrier in coulombs, $C$;
• and
• $v$ is the drift velocity of the charge carriers, $m{s}^{-1}$.

---

Derivation

Imagine a cuboid conductor of cross-sectional area $A$ and length $l$ with current flowing through it perpendicular to the cross section.

The material that makes the cuboid has, $n$ charge carriers per unit volume. As we are considering a metal conductor, these charge carriers are electrons, each with charge $e$.

The amount of charge per unit volume is en, and the volume is $Al$, so the total charge is $enAl$.

We can think of the electron travelling long the conductor with an average velocity of $v$, so the time taken, $t$ for the electron to travel the length, $l$ is $l/v$.

Now, the electric current is given by .

Substituting the above into the equation for current,

$$I=\frac{enAl}{l/v}$$

Which simplifies to

$$I=Aenv$$

As required

---

Potential Difference and emf

Prerequesite Materials:

Work Done

Charge and Current
(care of mmerevise.co.uk)

---

Describing Potential Difference

$V=\frac{W}{Q}$

• where
• $V$ is the potential difference across the component in volts, $V$;
• $W$ is the work done by the charge passing through the component in joules, $J$;
• and
• $Q$ is the amount of charge passing through the component in coulombs, $C$.

The voltage is a general term for potential difference and emf and where the context is clear can be used in stead of these.

---

Questions:

Current, Potential Difference and Resisitance
(care of www.savemyexams.com)

---

Electromotive Force (emf)

$V=\frac{W}{Q}$

which looks the same as potential difference, but here $W$ is the work done on the charge passing through a supply of energy.

---

Further Study:

Kirchhoff's Laws
(Care of isaacphysics.org)

Potential Dividers

---