What is the formula which links the p. d What is the formula which links the p.d. across a component and the current through the device? Describe an experiment you could use to determine the current through a component at different p.d’s.

Investigating Resistance 12/06/2018 LO: Link the relationship between resistance, current and potential difference for a fixed resistor Investigate V, I & R for various circuit components

In pairs, set up the standard test circuit V Why is the variable resistor necessary?

Investigate how current varies with potential difference in a series circuit with a fixed resistor. -Draw a results table which includes currents in both directions -Plot a graph showing results -Calculate the gradient. How does this relate to the value of resistance of your resistor? -How are V, I & R related?

Resistance = Potential Difference Current R=V I The unit of resistance is volts per amp (V/A) What is this also called? Ohm (Ω)

Defining Resistance The resistance of a component in a circuit is the ratio of the _______ ________ across it and the _________ flowing through it. Defining the Ohm A resistance of one Ohm means there is ___ volt of potential difference per ___ amp of current.

Ohm’s Law: The current through a conductor is proportional to the potential difference across it, as long as physical conditions remain constant e.g.___________. Devices which obey Ohm’s Law are known as ohmic e.g. ___________ ___________.

1) What is the value of resistance of a buzzer which has a current of 5mA through it and 20V across it? 4000Ω 2) Voltmeters have a very high resistance of 10MΩ. What must the potential difference be for 5μA to flow through it? 50V 3) Extension – For the circuit in Qu1, calculate the charge which passes in half a minute and how many electrons this equates to (Elementary Charge = 1.6x10-19C). i) 0.15C ii) 9.38x1017 electrons (3s.f.) If finished Page 99 Qu2

Investigate the I-V relationships for: 1) A filament bulb 2) A silicon diode You will need to ensure you apply a positive (forward) and negative (reverse) current and have a minimum of 8 values. Average values should be plotted!

6V DC 10Ω Potentiometer A V

Is your circuit connected correctly? LED: LED should turn when moving variable resistor to one end Voltage should be positive Current should be positive Diode: There should be a significant amount of current when moving the variable resistor to one end Multimeter on 200mA setting with leads in bottom two holes Multimeter on 10A setting with leads in top and bottom holes

Filament Lamp: Resistance increases with temperature and therefore current because... - metal ions have more kinetic energy (vibrate more) - electrons have to travel around more ‘turbulent’ ions in the metal and collide with them more frequently, transferring more energy to them.

Diodes: Resistance high until a threshold p.d. is reached. Current can only travel in one direction. Must be drawn the correct way around in a circuit diagram LED’s(Light emitting diode): Work at low p.d.’s and switch on instantly when threshold p.d. reached. Much more efficient than filament lamps Robust, versatile (used in TV's, traffic lights etc) and have a long life.

**How does drift velocity change if resistance decreases? I=nAve V=IR **How does drift velocity change if resistance decreases? Assume V,n,A,e are constant) How does current change if number density increases? How does drift velocity change if cross sectional area increases? How does current change if resistance decreases?

Extension Qu3 Pg99 (Tricky!) Homework – Due Mon 8th February -Draw V(x)-I(y) graphs for completed experiments -Questions 2&4 Pg99 Extension Qu3 Pg99 (Tricky!)

Sketch IV and R/V graphs for the following: Ohmic conductor (e.g. Wire) at constant temp Filament lamp LED

V=IR Practice Go through homework pg99 Qu2&4 Kirchhoff’s Law’s Sheet (not qu9) Pg101 Qu2 – It’s a thinker but easy when you get it!

Calculate how many mm2 there are in 1m2