No matter what parameters are given in the problem statement, convert them to SI units.
If in the condition of the load resistance and allocated to her power, be guided by the following considerations:R=U/I where R is the resistance in Ohms, U - voltage, I - current intensity, A. P=UI, where P is power, W, U - drop voltage, I - current intensity, A. it follows that P=I^2*R, i.e., I^2=P/R, or I=sqrt(P/R). Hence, U=R(sqrt(P/R)) or, after simplifying the expression, U=sqrt(P)*sqrt(R), where U is the required drop in voltage across the load, R is the resistance in Ohms, P is power, W.
A much more simple case occurs if to find the drop in voltage is required, knowing the power and strength of the current. To convert the expression does not need, so I use the following formula: U=P/I,where U is the required drop in voltageIn P power allocated to the load, W, I is the current passing through the load A.
If you know the load resistance and passing through it a current, drop the voltage on it also calculate in one step:U=IR where U is the required drop in voltage, I - current flowing through the load, And R is the load resistance in Ohms.
In addition to the above the most common tasks in the textbooks there are also other that need to know the drop voltage on a segment of a long homogeneous rod, made of a material having a high resistance. To do this, first calculate the drop voltage throughout the length of the rod (if it's not given in the problem statement initially). Then subtract from each other the horizontal coordinates of the points, the drop of voltage between which is to be determined.
The voltage on the entire length of the rod divide by its length, then multiply by your calculated length and you will get a drop in voltage between the points. Such dividers are found in the instrument with a transformerless power supply and are used as network switches of the voltage - in this case, the simplicity of the design is sacrificed to efficiency and safety.
After completing the calculation, if necessary, translate the result into convenient for presentation units: volts, millivolts, kilovolts, etc.
Advice 2 : How to measure power consumption
Sometimes it is necessary to know the amount of energy consumed by one or a group of devices. You must obtain the value of instantaneous power consumption. Using this value is easy to calculate the consumed power for a certain period of time. There are several ways to solve this problem.
You will need
- AC voltmeter, AC ammeter, wattmeter.
In some cases, the instantaneous power consumption of the appliance stated in his passport data. To get the value of their consumption of electricity over a certain period of time, multiply the instantaneous energy consumed (in kW) of the device to the value of the period of time during which he worked (in hours). For example, when calculating the energy consumption of household with a TV with a power consumption of 80 Watt, who has worked for 3.5 hours, multiply the capacity of the TV (0,08 kW) time (3.5 hours). Get the value of the total energy consumed by the TV during this time: 0,08 × 3,5 = 0.28 kilowatt-hours. In the case when you need to calculate the total consumed power of the group of devices, the consumed power is first calculated for each device, then these values are summed.
To measure the instantaneous power consumption of the device turn on the parallel plug of the instrument AC voltmeter, series - ammeter in AC. Turn on the device. Count and multiply the obtained values of voltage and current. For example, the resulting voltage was 218 Volts, and the current is 0.75 Ampere: 218 × 0,75 = 163,5 Watt. Multiply this value by the amount of time during which he worked (e.g. 6 hours) and get the value of the consumed power: 0,1635 × 6 = 0,981 per kilowatt-hour.
With the availability of modern household wattmeter plug it into an electrical outlet. Then connect the measured consumer current in the socket located on the housing of the power meter. Consider the value of the instantaneous energy consumption. On some models, the power meter further specify the value of energy consumed since the inclusion of time.