Series and parallel circuits When designing and building circuits it is important to consider how the components will be connected. In a simple circuit they can be connected in series or in parallel. In a series circuit there is only one path along which electrons can flow. In a parallel circuit there is more than one path. Some circuits use a combination of series and parallel circuits.
- + Fig. 10 A series circuit.
- + Fig. 11 A parallel circuit.
Activity Set up the circuit as shown in Fig. 10 with the two bulbs connected in series. Observe the brightness of the bulbs. Using the same components arrange the bulbs as shown in Fig. 11 with the bulbs connected in parallel. Observe the brightness of the bulbs. In which type of circuit do the bulbs shine more brightly?
Activity
Design and build simple circuits that can perform the following: Switch two bulbs on and off at the same time. Switch either of two bulbs on or off. Switch on three bulbs with one bulb brighter than the other two.
1. 2. 3.
31.5 Voltage, current and resistance: Ohm’s Law
Georg Ohm (1789–1854) was a German scientist. Using evidence from many experiments he defined the relationship between voltage, current and resistance. This is now known as Ohm’s Law. Ohm’s Law states that when the temperature is constant the amount
of steady current (I) passing through a material is directly proportional to the voltage across the material (V), so the greater the voltage, the greater the current. Ohm discovered that you can calculate the resistance (R) of the material if you divide voltage (V)
Fig. 12 Georg Ohm.
by current (I). Resistance is affected by temperature so Ohm’s Law is true only if the temperature stays the same. Ohm’s Law can be summarised as:
V I = R
I X R V
340
V = I X R I = V/R R = V/I
Fig. 13 The ‘Very Important Rule’ triangle. Memory Tip ‘Very important rule’
