Resistors in series and parallel

AIM                                                                                                               

To determine the effect of resistors connected in series and parallel on potential difference and current in the circuit.

HOW DOES IT WORK?                                                                                   

Time Allocation: 45 Min

When resistors are connected in series, there is only one path for current to flow. This ensures that the current is the same at every point in the circuit. The potential difference is divided across the resistors and the sum of each individual resistor’s potential difference is equal to the potential difference across the battery. If resistors are connected in parallel, there are more paths for the current to flow. The current splits across the different paths. The potential difference is the same across the resistors and the battery. The sum of the current in each parallel section is equal to the current in the main circuit.

APPARATUS

• 3 x Torch cells (1,5 V)
• 2 x small light bulbs
• 1 x Ammeter
• 1 x Voltmeter
• 8 x connecting leads
• 1 x Switch

METHOD:                                           

1. Set up a circuit as shown in the diagram.
2. Take the readings on the ammeter and voltmeter when the switch is closed for a short period of time.
3. Change the position of the ammeter. I_B between the bulbs; I_C between the bulb and switch (I_C); I_D between the switch and battery. Note the readings of the ammeter in a table.
4. Reset the ammeter to the original position and change the position of the voltmeter. V₁ across bulb 1; V₂ across bulb 2; V₃ across both bulbs. Note the readings in a table.
5. Change the layout of the circuit so that the bulbs are in parallel, as shown in the diagram
6. Take the readings on the ammeter and voltmeter when the switch is closed for a short period of time. Change the position of the ammeter to measure the current strength in each parallel circuit. Note the readings of position I_F and I_G.
7. Change the position of the voltmeter the cells V_s, across bulb 1, and across bulb 2. Note the reading of V_s, V₅ and V₆

NOTE: To ensure accurate readings:

• Use batteries with negligible internal resistance.
• Take readings quickly and wait between consecutive readings. If the temperature in the wires increases, the resistance in the wires will increase and it will have an impact on the results.
• Make sure that learners know how to connect ammeters and voltmeters and how to take readings.
• Connect the positive terminal of the ammeter and voltmeter closest to the positive terminal of the battery – this will prevent unnecessary damaging of the meters.
  • If the ammeter has different scales, connect to the positive terminal that provides the largest scale. If the reading is small enough to fit on a smaller scale, move the connector to the smaller scale.

PRECAUTIONS:

• Do not allow leads from the battery, to touch. The circuit will be short-circuited and components may be damaged.
• Do not touch connectors with bare hands.