1. Electrical Measurements Lab Manual
2. Electrical Measurements Lab Manual Jntuk
3. Electrical Measurements Units

Electrical Measurements Introduction In this section, electrical measurements will be discussed. This will be done by using simple experiments that introduce a DC power supply, a multimeter, and a simplified way to represent electric circuits using a schematic diagram. Mass and Electric Charge, Mass Flow and Electric Current Matter has a number of properties, including mass and electric charge. Mass, M (measured in kilograms, kg), is a positive quantity. Electric charge, Q (measured in coulombs, C), on the other hand, can be either positive or negative.

The net electric charge is the sum of the charge from the positively-charged ion cores and the negatively-charged electrons. Under ordinary circumstances, the positive and negative electric charges of a piece of matter cancel out, leaving it neutral. An increase in the net electric charge can occur either by increasing the amount of positive charge or by decreasing the amount of negative charge. For ordinary metals, the positive ion cores are immobile and the electrons constitute the 'electric fluid.' For constant mass flow rates, the mass of fluid that flows through a pipe equals the rate of mass flow (or mass current) multiplied by the time. Similarly, for constant charge flow rates, the charge, Q, that flows through a wire equals the rate of charge flow (or electric current, I, measured in amperes, A) multiplied by the time, t. Q = It Reservoirs and Capacitors, Pressure and Voltage, Pumps and Power Supplies Water is often stored in a reservoir or a water tower.

We may think of a reservoir as a tank of water that is under pressure. When two reservoirs at different pressures are connected by a pipe, the pressure difference causes water to flow through the pipe from the higher to the lower pressure reservoir. Similarly, electric charge can be stored in electrical reservoirs, called capacitors, which are metal plates that may be thought of as being under an electric pressure, called voltage.

When two metal plates at different voltages are connected by a wire, the voltage difference causes an electric current to flow through the wire from the higher to the lower voltage plate. A high water pressure can be produced with a water pump attached to the reservoir, quickly replacing any water that is used, so that the water pressure does not decrease.

The electrical equivalent of a water pump can be a single voltaic cell (an ordinary 1.5 volt D cell), a battery of voltaic cells (a 12 volt car battery), a power supply, etc. Pipes and Wires, Resistance, Circuits Water flows easily within a pipe, flows slowly through soil, and does not flow at all through the walls of a pipe (unless the pressure in the pipe is high enough to cause the pipe to burst). Similarly, electric charge flows easily along metallic wires, flows slowly along moistened paper (this property is used in electrophoresis, which is employed for DNA fingerprinting), and does not flow at all out of the material that clads a wire, or from the wire to the air (unless the voltage of the wire is so high that it causes electrical breakdown).

Electrical Measurements Lab Manual

The cladding is said to have more electrical resistance than the wire. When we connect a hose from a high pressure to a low pressure reservoir, initially the water can flow easily. Eventually, however, the pressures equalize, and no flow can occur. If we want continuous flow through a pipe, and we do not have an infinite amount of water in our reservoirs, we put a pump in the pipe, and we recirculate the water by including a return pipe, thus forming a closed circuit. We do a similar thing with electricity when we use a power supply to drive electric current through a closed electric circuit. Before we begin, we need to review a few new concepts that you will need to perform this lab.

Current, Voltage and Resistance Although you are just beginning your study of static electric charges, when these same charges move around in a circuit they produce an electrical current which is the rate of flow of charge. The SI unit for current is the ampere (A) = 1 Coulomb/sec. By convention, the direction of the current is the direction of flow of positive charge, even though in metallic conductors the current is due to flow of negative charge (electrons) in the opposite direction.

Because of conservation of charge, the current is the same at all points in a single loop circuit. At a branch point in a circuit, where the conducting path splits into two or more paths, the total current into a branch point equals the total current out of that point.

To produce these moving charges we will use either a battery or a power supply, which uses chemical or electrical energy respectively to push these charges around a circuit. By convention, current flows out of the positive terminal of a battery or power supply and into the negative terminal. For current to be maintained in a circuit there must be a complete conducting path. Voltage is a measure of the electric potential difference between two points in a circuit and the difference in potential between two points in a circuit causes these electrical currents to flow. The SI unit for potential is the volt (V). Since the electrical force is a conservative force, the sum of the voltage increases and decreases around any closed loop is zero.

Resistance is the property of a circuit element (conductor) to oppose current flow. Resistance is defined. R = V I, where V is the voltage across the circuit element and I is the current flowing through it. If R is constant, the same for all V, then the circuit element obeys Ohm's Law. The SI unit of resistance is the ohm ( Ω). The resistance of a resistive circuit element changes with temperature.

Series and Parallel Circuits Two resistors R 1 and R 2 are connected in series if all the current that passes through R 1 also passes through R 2. Therefore, for two resistors in series the current I 1 through R 1 is the same as the current I 2 through R 2, and this current is the same as the current, I, that enters the series network. R p = R 1 R 2 R 1 + R 2.

Ammeter and Voltmeters Ammeters are used to measure current. An ammeter is connected in series with the circuit so that all the current being measured flows through the ammeter. Therefore, ammeters need to have very small resistance in order not to alter the current in the circuit.

Voltmeters are used to measure voltages. A voltmeter is connected in parallel at the two points between which the potential difference is to be measured. Therefore, a voltmeter needs to have a large resistance so that very little current is diverted through it. 1 The power supply is a source of voltage difference. Locate the DC power supply at your lab table. Press the POWER On/Off button to the ON position. Next, press the RANGE button to the IN (0.85 A) position (this sets the power supply to the 0-35 V/0-0.85 A range).

Rotate the voltage and current ADJUST knobs fully counterclockwise. Then set the maximum output current for this experiment by pressing the CC Set button, and while holding it down, rotate the current ADJUST knob clockwise until the AMPS display reads 0.20. Release the CC Set button. Do not move the current setting knob ( CC Set) after this adjustment (unless given instructions in the lab).

3 To turn on the multimeter, toggle the top left button on the meter until there is a display on the meter face. To set up the multimeter to measure DC voltage differences, ΔV, abbreviated as V on the meter, toggle the top right button to DC. Be sure that the meter display reads DC. Turn the Function/Range switch to the voltage (V) range and dial setting to 20. The meter is now set to read voltages up to 20 volts DC.

Attach banana-banana leads to the common (COM) jack and to the voltage (V) jack. 7 We now perform a more quantitative study of properties of the light bulb. TURN THE POWER SUPPLY VOLTAGE TO ZERO but do not turn off the power supply.

Do not readjust the current setting ( CC Set). We will use the multimeter to measure the DC current through the light bulb as a function of the applied voltage. To do this, we must connect the multimeter in with the light bulb, so that the same current passes through both.

Electrical Measurements Lab Manual Jntuk

This is your first current measurement: since it is easy to blow a fuse on the current setting, follow instructions carefully. 12 Using the Excel worksheet from of the Resistor section, plot your current data points vertically and the voltage difference horizontally. This choice of axes is made because the voltage difference is the independent variable; it causes the current. Do not forget to label the axes. If you get results as expected, the data will not lie on a straight line: the response (the current) caused by the voltage difference is not linear.

Electrical Measurements Units

This can be traced to the fact that the tungsten filament in the light bulb is heating up. Find a reference (textbook, website, etc.) about a tungsten filament and review the explanation as to its properties.