As you may have noticed, the two parallel plates more closely resemble the uniform gravitational field from Figure 1, with the main difference being that the electric field can exist in any direction - unlike the gravitational field, which only moves down toward the Earth. If you look at Figure 2 below, you will notice that a point charge produces a field that emanates radially from the point, whereas the two parallel plates that have charges placed on them produce a uniform field between them. Also, the shape of the field depends on the shape of the object producing the field. Since we know opposites attract, a positive test charge will move toward the negative side of the electric field. On the other hand, for an object with charge in an electric field, the direction of the force depends on whether the charge is negative or positive. Another difference between electric and gravitational fields is that an object with mass always experiences a force in the direction of the gravitational field (i.e., down toward the floor for any object near the Earth’s surface). The unit used to measure the amount of charge in a test charge is the coulomb (C), akin to the unit of mass used for the ball, which is kilograms (kg). Just as a ball can have different amounts of mass depending on the type of ball (baseball, basketball, etc…), a test charge can have different amounts of charge depending on the source. An electric field is produced around any source of electric charge. If a test charge is placed in an electric field, it will move just like the ball moves in a gravitational field because the electric field interacts with the charge of the test charge in much the same way that gravity interacted with the mass of the ball in the previous example. In an electric field, a test charge is analogous to the ball in the gravitational field. The force exerted by the field on the ball is F = m g ( force =mass of the ball x gravity) Figure 1.Īn electric field is a bit different because in order to interact with the field you need to use what is commonly referred to by physicists as a test charge. We assume, for the most part, that the gravitational field experienced by the ball is uniform, therefore, the ball falls straight from your hand to the ground. This happens because the ball is in a gravitational field and the gravitational field produced by the Earth interacts with the mass of the ball. If we take a ball (basketball, golf ball, baseball, etc.) and drop it, we see that it falls toward the Earth. The concept of the electric field is a bit esoteric compared to, let’s say, a gravitational field because we can interact much more easily with a gravitational field than we can with an electric field. For this lesson we will focus on the electromagnetic force, specifically the force produced by an electric field (E). The four forces are gravitational, electromagnetic, strong nuclear and weak nuclear. There are four fundamental interactions that occur in nature in physics they are referred to as fundamental forces. This activity requires about 1-1.5 hours to complete.
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