Fill in the gaps for the unknown Voltage and current readings b) c) d) e)

Current & Ammeters Investigation Place an Ammeter at various point in a circuit with one bulb and measure the current flow Repeat with two bulbs in series Repeat with two bulbs in parallel 1. 2. For each task draw a circuit and record the current values at each point (either side of a light bulb) measured in the circuit. 3. What can you conclude about Current in S & P circuits ???

What can you conclude about Voltage in S & P circuits ??? Voltage investigation Investigation: Set up a circuit with one bulb and measure the Voltage drop across the bulb (V1) and power supply (Vs) 2. Repeat with two bulbs in series, measure V1 V2 and Vs 3. Repeat with two bulbs in parallel, measure V1 V2 and Vs For each task draw a circuit and record the voltage values for each component, then comment on your observations (ie bulb brightness). What can you conclude about Voltage in S & P circuits ???

Circuit in series In a series circuit, each device is connected in a manner such that there is only one pathway.

The electrons move with the same speed anywhere in the circuit Current in a series circuit is constant. I1 = I2

It does NOT matter where the current is measured, or where the ammeter is placed I = I1 = I2 Proved! Make this circuit and prove the above Theory!

Voltage in series circuits Voltage in a series circuit is shared between the resistances. That’s why the light bulbs get dimmer when we add another light bulb to the circuit

V & I in a (series) circuit

I = Vs/R Basic Circuit: Series Circuit: V1 + V2 = VS RT = R1 + R2 Current (I) has the same value everywhere in the circuit RT = R1 + R2 I V1 + V2 = VS RT Vs I I = V/RS

Equivalent Series Resistance 12 W a b 4 W 8 W a b

What is the series resistance? 4 16 V 4 What is the series resistance? Calculate the current in this circuit.

Ex: 47  V 28  The current through the 47  resistor is 0.12 A Calculate the voltage V of the battery.

A V I R The supply voltage is 12 V. The potential drop across the lamp is 4.0 V The current I = 3.0 A. Calculate the resistance R A V I R The supply voltage = 12 V (A potential rise (PR)) The voltage across the resistor + lamp = 12 V (A potential drop (PD)) The voltage drop across the ammeter is insignificant. Mathematically 12 V = VR + 4 V rearranging VR = 12 - 4 = 8 V

For some Christmas lights, if one bulb is blown, the whole string goes out. For others, one bulb can go out and the rest stay lighted. What is the difference ?

Circuits in parallel In a parallel circuit, each device is placed in its own separate branch.

Voltage in parallel circuits A Voltmeter is always connected in parallel with the component

The brightness of the light bulb does NOT change when we add another bulb in parallel

Voltage across the light bulb is the same as the voltage in the battery. V1 = V2 Proved! Make this circuit and prove the above Theory!

Current in parallel circuits The current is shared through the resistances in a parallel circuit Make this circuit and prove the above Theory! Proved!

V & I in a (Parallel) circuit

In a series circuit, the current is the same through each resistor V R2 In a series circuit, the current is the same through each resistor R1 V R2 In a parallel circuit, the voltage is the same across each resistor

Parallel Circuit: Ic = I1 + I2 VBatt = VR1 = VR2 I1 = V/R1 I2 = V/R2 ? I1 = V/R1 I2 = V/R2 RP V I1 Ic = V/RP

(RP < R1 , R2)!!! Resistors in Series RS = R1 + R2 Resistors in Parallel R1 R2 (RP < R1 , R2)!!!

Equivalent Parallel Resistance 6 W 30 W a b 5 W a b

What is the parallel resistance? 16 V 4 4 What is the parallel resistance? Calculate the current in all branches of this circuit.

Ex: V 47  28  The current through the 47  resistor is .12 A Calculate the current through the 28  resistor.

Circuit solving 13.7 V 3 A R A car battery has a voltage of 13.7 V. The current I = 3 A. The resistors are identical. Calculate the resistance of each resistor (R). To find the total resistance (RT) of the circuit

Excellence The supply voltage is 12 V. The current I = 2.0 A. The resistors are identical. Show the resistance of each resistor is 12 Ω Excellence