Calaculate the resister value for a load which requires 4om A and 12 v for its function ,which haves an input voltage of 24v
Answers
Answer:
Explanation:
Voltage Divider Circuits are useful in providing different voltage levels from a common supply voltage. This common supply can be a single supply either positive or negative, for example, +5V, +12V, -5V or -12V, etc. with respect to a common point or ground, usually 0V, or it could be across a dual supply, for example ±5V, or ±12V, etc.
Voltage dividers are also known as potential dividers, because the unit of voltage, the “Volt” represents the amount of potential difference between two points. A voltage or potential divider is a simple passive circuit that takes advantage of the effect of voltages being dropped across components which are connected in series.
The potentiometer, which is a variable resistor with a sliding contact, is the most basic example of a voltage divider as we can apply a voltage across its terminals and produce an output voltage in proportion to the mechanical position of its sliding contact. But we can also make voltage dividers using individual resistors, capacitors and inductors as they are two-terminal components which can be connected together in series.
Resistive Voltage Divider
The simplest, easiest to understand, and most basic form of a passive voltage divider network is that of two resistors connected together in series. This basic combination allows us to use the Voltage Divider Rule to calculate the voltage drops across each series resistor.
Resistive Voltage Divider Circuit
voltage divider network
Here the circuit consists of two resistors connected together in series: R1, and R2. Since the two resistors are connected in series, it must therefore follow that the same value of electric current must flow through each resistive element of the circuit as it has nowhere else to go. Thus providing an I*R voltage drop across each resistive element.
With a supply or source voltage, VS applied across this series combination, we can apply Kirchhoff’s Voltage Law, (KVL) and also using Ohm’s Law to find the voltage dropped across each resistor derived in terms of the common current, I flowing through them. So solving for the current (I) flowing through the series network gives us:
voltage divider current
The current flowing through the series network is simply I = V/R following Ohm’s Law. Since the current is common to both resistors, (IR1 = IR2) we can calculate the voltage dropped across resistor, R2 in the above series circuit as being:
voltage drop resistor R2
Likewise for resistor R1 as being:
voltage drop resistor R1
Voltage Divider Example No1
How much current will flow through a 20Ω resistor connected in series with a 40Ω resistor when the supply voltage across the series combination is 12 volts dc. Also calculate the voltage drop produced across each resistor.
voltage divider example
Each resistance provides an I*R voltage drop which is proportionaly equal to its resistive value across the supply voltage. Using the voltage divider ratio rule, we can see that the largest resistor produces the largest I*R voltage drop. Thus, R1 = 4V and R2 = 8V. Applying Kirchhoff’s Voltage Law shows that the sum of the voltage drops around the resistive circuit is exactly equal to the supply voltage, as 4V + 8V = 12V.
Note that if we use two resistors of equal value, that is R1 = R2, then the voltage dropped across each resistor would be exactly half the supply voltage for two resistances in series as the voltage divider ratio would equal 50%.
Another use of a voltage divider network is that to produce a variable voltage output. If we replace resistor R2 with a variable resistor (potentiometer), then the voltage dropped across R2 and therefore VOUT can be controlled by an amount dependant on the postion of the potentiometers wiper and therefore the ratio of the two resistive values as we have one fixed and one variable resistor. Potentiometers, trimmers, rheostats and variacs are all examples of variable voltage division devices.
We could also take this idea of variable voltage division one step further by replacing the fixed resistor R2 with a sensor such as a light dependent resistor, or LDR. Thus as the resistive value of the sensor changes with changes in light levels, the output voltage VOUT also changes by a proportional amount. Thermistors and strain guages are other examples of resistive sensors.
Since the two voltage division expressions above relate to the same common current, mathematically they must therefore be related to each other. So for any number of individual resistors forming a series network, the voltage dropped across any given resistor is given as: