First-hand InvestigationResistance

Aim:To investigate and compare the current-voltage relationship for a small incandescent lamp with the current-voltage relationship for a resistor of the type used in many electronic devices and to calculate the power produced by these components in different circumstances.

/ Method: Use the circuit on the left to investigate the voltage-current relationship for a 36W lamp. The circuit consists of lamp, variable voltage power supply, ammeter and voltmeter.
Use the T-R unit voltage selector to vary the voltage.
An appropriate meter and meter range must be chosen for each set of measurements.
CAUTION – wire the ammeter in series and the voltmeter in parallel with the lamp. Check that you have the meter connected using the correct polarity before you turn on the voltage.
Record the measurements in an appropriate table[1].
Record the specifications of the lamp …………………….…………… (do it now! You’re gonna need it later)
/ Repeat the investigation using a resistor (image below shows a typical resistor with colour code brown/black/red/silver).
Record the colour code of the resistor …………………….…………

Analysis and questions (Show question numbers clearly in your report and show full working)

  1. Graph the measurements for the lamp and the resistor on separate graphs with voltage on the vertical axis.
  2. Describe in words the relationship between the measured variables for each graph[2].
  3. Resistance (R) is defined as the ratio voltage/current and it is measured in ohms ().

(a)Calculate the resistance of the resistor for voltages of 6 V and 12 V using the graph for the resistor.

(b)Compare your calculated value with the nominal value (determined from the colour code)

(c)Calculate the resistance of the lamp for voltages of 6 V and 12 V using the graph for the lamp.

(d)Compare the devices in terms of the calculated resistances.

  1. Power (P) is equal to the product (voltage x current). Power is measured in watts (W). Current must be in amperes and voltage in volts when doing this calculation.

(a)Calculate the power produced by the resistor when a voltage of 6 V and 12 V is applied across it.

(b)Calculate the power produced by the lamp when a voltage of 6 V and 12 V is applied across it.

  1. Calculate the total charge that passes through the lamp in one minute when the voltage across it is 12V.
  2. Write a concise conclusion in terms of the aim of this investigation.

Research

(A)Explain the shape of the voltage-current graph for the lamp.

(B)Compare the nominal specifications (manufacturer’s specifications) for the lamp with the value you have measured. Propose which you think is correct and justify your proposition.

(C)Describe typical uses of resistors in the home.

Resistor

resistor, two-terminal electric circuit component that offers opposition to an electric current. Resistors are normally designed and operated so that, with varying levels of current, variations of their resistance values are negligible. They are available in several common forms: wire-wound resistors are formed from windings of fine wire; film resistors, commonly found in consumer electronic devices, use lengths of carbon or metal film deposited on a resistive base; and carbon-composition resistors use a bonded mass of carbon powder with a phenolic binder. Some resistors are made so that their values can be adjusted. Resistors transform electrical energy in a circuit into heat energy; they are normally rated for the maximum amount of power that they can safely handle without the resistor being destroyed.

An incandescent light globe is an example of a household resistor.

Resistor Colour Code

Resistors used in electronic circuits often use a colour code to represent their resistance. This code is illustrated in the following diagram.

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[1] Rule up table neatly – rows and columns – Use table heading – Show quantities and units

[2]Heading on graph – axes labeled (quantities and units) – data plotted in pencil “X” - LOBF