Electric motors are everywhere in our daily lives. You might use one to power your toothbrush or cool your computer. They even start the engine in some cars! It's amazing that they can convert electric energy into mechanical energy with just one moving part. This article will teach you the basics of how electric motors work, including their components, different types, and how they're used. So let's dive in and learn more about the fascinating world of electric motors! Don't miss out on this essential knowledge if you want to understand the technology that surrounds us every day.
In simple terms, an electric motor works by converting electrical energy into mechanical energy. This is done through the interaction of a stationary magnetic stator and an electromagnetic rotor in DC motors. When a wire carrying an electrical current is placed in a magnetic field, it generates a force known as the motor effect. The force depends on the strength of the magnetic field, the length of the wire, and the amount of current passing through it. The motor effect is strongest when the wire and magnetic field are at a 90° angle to each other, and it decreases to zero when they're parallel. This is the basic principle behind how an electric motor works.
is the force in newtons
is the magnetic flux density in tesla
is the current in ampere
is the conductor length in meters
Fleming's Left-Hand Rule is a handy trick for figuring out the direction of force on a currentarrying wire in a magnetic field. Simply hold your left hand with your thumb, index finger, and middle finger at right angles to each other. Then, point your index finger in the direction of the magnetic field and your middle finger in the direction of the current flow. Your thumb will then point in the direction of the force on the wire.
When it comes to electric motors, there are two main types: AC motors and DC motors. There are many different designs for each type, depending on the specific application.
The simplest form of DC motor consists of a stationary magnetic field and a conductor coil connected to a split ring commutator, which is connected to a DC power supply via brushes. The diagram below shows this type of motor in a starting position.
A DC motor works by applying a voltage to the brushes, which passes the voltage to the coil through the split ring commutator. The current-carrying coil is in a magnetic field, which produces a rotational force on the coil. The split ring commutator is used to switch the current direction in the coil at the same rate as the motor rotates. To increase the power of a DC motor, the strength of the magnetic field can be increased, more turns can be added to the coil, or a higher current can be used in the coil. A more advanced type of DC motor is the brushless motor, which uses a semiconductor controller to vary the DC supply voltage polarity. This provides better performance and improved reliability, as the brushes in brushed motors often wear out and need to be replaced.
AC motors work using a similar principle to DC motors, but with several key differences. Generally, the coil windings form the stator (stationary part) of the motor, while the rotor is a permanent magnet or electromagnet. In an AC motor, an alternating current (AC) is applied to the stator coil windings, creating a varying magnetic field. This varying magnetic field is used to produce a rotational force on the rotor, spinning the motor. The split-ring commutator is no longer needed, since the current direction is reversed by the AC supply.
The AC motor works on the principle of electromagnetic induction. When an alternating current is applied to the stator windings, the varying magnetic field created by the current induces a voltage in the rotor windings. This voltage then produces a current in the rotor windings, creating a magnetic field that interacts with the stator field to produce a torque that rotates the rotor.
The AC motor also has several advantages over DC motors. For example, AC motors are more efficient and can produce more power than DC motors. Additionally, AC motors can be used in applications where the speed of the motor needs to be controlled, such as in electric vehicles.
Electric motors are ubiquitous in our daily lives, powering devices we use every day. DC motors are commonly used in battery-powered household devices like electric toothbrushes, remote-controlled cars, and battery-powered drills, while motors are used in mains-powered devices like extractors fans, vacuum cleaners, and washing machines. The choice of motor type is often dictated by the power supply, as it's more efficient and cost-effective to use an AC motor in a mains-powered device and a DC motor in a battery-powered device, to avoid the need to convert power supplies.
When calculating the power of an electric motor, there are two variables you should consider, the output power and the input power.
That's a great experimental design to measure the output mechanical power of a motor! As you mentioned, the mechanical power of the motor is the output power of the motor, and it can be calculated by dividing the amount of useful work done by the time taken to complete the work.
To calculate the work done by the motor, we can use the equation you mentioned:
Work = Force x Distance
In the experimental setup you suggested, we can lift a known mass (m) by winding it up on a string using the motor. The force required to lift the mass is equal to the weight of the mass, which can be calculated using the equation:
Force = mass x gravity
where gravity is the acceleration due to gravity (9.8 m/s^2).
Once we know the force required to lift the mass, we can calculate the work done by the motor to lift the mass a certain distance (d) using the equation:
Work = Force x Distance
Once we have calculated the work done, we can find the mechanical power of the motor by dividing the work done by the time taken to complete the work.
Mechanical Power = Work done / Time taken
By measuring the time taken to lift the mass and calculating the work done, we can determine the mechanical power output of the motor. This information is useful in determining the efficiency of the motor, as well as in selecting and designing motors for different applications.
The electric motor input power can be found using the general electric power equation. Note that this can be done because the input power of an electric motor is electrical power.
Great example! Let's use the given information to calculate the input power, output power, and efficiency of the motor in lifting a weight.
We know that lifting a weight (mass) of 10 kg to a vertical distance of 2 meters requires 196 J of work (W = mgh, where g is the acceleration due to gravity, which we assume to be 9.8 m/s^2).
We also know that the motor draws 2 A of current at 120 V for 10 seconds to lift the weight. Using Ohm's law (V = IR), we can calculate the resistance of the motor as:
R = V / I = 120 V / 2 A = 60 ohms
The input power of the motor is given by:
P_input = VI = (120 V)(2 A) = 240 W
The output power of the motor is given by:
P_output = W / t = 196 J / 10 s = 19.6 W
The efficiency of the motor is given by:
Efficiency = P_output / P_input x 100%
Efficiency = 19.6 W / 240 W x 100% = 8.17%
So, the input of the motor is 240 W, the output power is 19.6 W, and the efficiency of the motor is 8.17%. This means that only about 8% of the electrical energy input is converted into useful mechanical work, with the rest being lost as heat due to the resistance of the wire coils and friction between moving and static components.
Electric Motors - Key takeaways Electric motors work due to a phenomenon called the motor effect. The motor effect is the force generated on a current-carrying wire as it passes through a magnetic field. The strength of the force can be increased by increasing either the magnetic field strength, current in the wire, or the length of wire in the magnetic field. A DC motor uses a split-ring commutator to reverse the direction of the current in a wire coil every half-turn. This ensures the forces on the wire coil always continue to accelerate the coil's rotation and spin the motor. An AC motor also uses the motor effect to spin but uses an AC power supply to vary the current direction instead of the split-ring commutator. Typically AC motors have the coil windings in the stator, and a permanent magnet or electromagnet rotor. The efficiency of an electric motor can be calculated by measuring how much input energy is needed to perform a known amount of work.
How to calculate electric motor power?
Electric motor power can be calculated by measuring the time taken to do a known quantity of work. For example, lifting a 5N weight by 1m requires 5J of work. If the motor performs this work in 2 seconds, the output power can be calculated as 5J / 2S = 2.5W.Alternatively, if the output shaft torque and rotation speed can be measured, mechanical power can also be calculated as:Power = torque x rotational velocity,where torque is measured in Nm and rotational velocity in radians per second.
What is the science behind electric motors?
Electric motors utilise the motor effect, which produces a force on a current carrying wire in a magnetic field. In a DC motor, a coil of wire is used so that each side experiences an opposite direction force in the magnetic field, causing the coil to rotate. Every half-turn, a split ring commutator flips the voltage polarity on the coil, reversing the current direction. Fleming’s left hand rule shows that this reverses the direction of the forces on the coil, ensuring it continues to be rotationally accelerated. Brushes are used to transfer the DC power supply to the rotating split-ring commutator.
What is electric motor and its efficiency?
The electric motor is an electro-mechanical device which converts input electric power to output mechanical power. To calculate efficiency, the proportion of input energy that is converted to useful output work must be calculated using the following equation:Efficiency = (Useful output power) / (Input Power)Which can also be represented as:Efficiency = (Useful Mechanical Power) / (Electrical Power)
How does an electric motor work?
Electric motors utilise the motor effect, which produces a force on a current carrying wire in a magnetic field. In a DC motor, a coil of wire is used so that each side experiences an opposite direction force in the magnetic field, causing the coil to rotate. Every half-turn, a split ring commutator flips the voltage polarity on the coil, reversing the current direction. Fleming’s left hand rule shows that this reverses the direction of the forces on the coil, ensuring it continues to be rotationally accelerated. Brushes are used to transfer the DC power supply to the rotating split-ring commutator.
