Current Measuring Device has Finite Non-zero Resistance

# Materials Required

• Cell
• Key
• Rheostat
• Ammeter
• Digital multimeter (DMM)

# The Procedure

## Real Lab Procedure

• Make a circuit using a cell, key, rheostat, ammeter, and a digital multimeter (DMM).
• Connect the positive terminal of the battery to the ammeter.
• Connect the lower end of a rheostat to the negative terminal of the ammeter.
• Connect the upper end of the rheostat to the key.
• Connect the key to the negative terminal of the battery.
• Connect a multimeter across the ammeter.
• Switch on the cell.
• Close the key and then adjust the rheostat so that a current of the order of 1 A flows through the ammeter.
• Observe the voltage drop (V) across the ammeter with the voltmeter DMM in dc mV range.
• Find the resistance of the ammeter by the ratio of the voltage drop V to the ammeter reading, [R = V/ I] ohm.
• Repeat the procedure for different ammeter readings and calculate the mean value of the resistance.

# Simulator Procedure

• Click on the check box to show/hide the circuit diagram and connect the circuit.
• Drag and drop the wire from the +ve end of the cell to +ve end of Ammeter.
• Drag and drop the wire from the –ve end of the cell to the key.
• Drag and drop the wire from the key to the upper end of rheostat.
• Drag and drop the wire from the –ve end of the ammeter to the lower end of the rheostat.
• Drag and drop the wire from the +ve end of the ammeter to the +ve end of the digital multimeter.
• Drag and drop the wire from the -ve end of the ammeter to the -ve end of the digital multimeter.
• Drag and drop the key into the key holder.
• Move the rheostat slider by using the slider.
• Note reading in ammeter and Digital multimeter.
• Click on the Show Result button to view the results.
• Repeat the above procedure by moving the slider.
• Click on the Next button.
• Observe the observation table.
• Click on the next button after referring to the observation table.
• Repeat the above procedure using another ammeter.
• Click on the Inference button to show the observation.
• Click on the reset button to redo the experiment

# Observations

 Sl.no Current(A) Multimeter reading (mV) Resistance (Ohm)