12/3/2023 0 Comments Electric flux formula problems![]() The distance r in the denominator is the distance from the point charge, Q, or from the center of a spherical charge, to the point of interest. This equation gives the magnitude of the electric field created by a point charge Q. Mathematically, saying that electric field is the force per unit charge is written asġ8.16 E = F q test = k | Q | r 2. For example, if we double the charge of the test charge, the force exerted on it doubles. The force exerted is proportional to the charge of the test charge. The electric field exerts a force on the test charge in a given direction. A test charge is a positive electric charge whose charge is so small that it does not significantly disturb the charges that create the electric field. ![]() Now consider placing a test charge in the field. The electric field extends into space around the charge distribution. The charge distribution could be a single point charge a distribution of charge over, say, a flat plate or a more complex distribution of charge. If you know the electric field, then you can easily calculate the force (magnitude and direction) applied to any electric charge that you place in the field.Īn electric field is generated by electric charge and tells us the force per unit charge at all locations in space around a charge distribution. Michael Faraday, an English physicist of the nineteenth century, proposed the concept of an electric field. For example, the gravitational field surrounding Earth and all other masses represents the gravitational force that would be experienced if another mass were placed at a given point within the field. The concept of a field is very useful in physics, although it differs somewhat from what you see in movies.Ī field is a way of conceptualizing and mapping the force that surrounds any object and acts on another object at a distance without apparent physical connection. You may have heard of a force field in science fiction movies, where such fields apply forces at particular positions in space to keep a villain trapped or to protect a spaceship from enemy fire. Create and interpret drawings of electric fields. ![]() Calculate the strength of an electric field.By the end of this section, you will be able to do the following:
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12/3/2023 0 Comments Android life cycle turn off device![]() Permission to bind to an accessibility service:.The following three required items are declared in AndroidManifest.xml: Information about the accessibility service is declared in the manifest: Here is a walkthrough of the contents of each file. app/src/main/java/com/example/android/globalactionbarservice/ GlobalActionBarService.java.app/src/main/res/xml/ global_action_bar_service.xml.app/src/main/res/layout/ action_bar.xml.All the code you'll write in this codelab is restricted to the following four files: ![]() The bare-bones skeleton for the accessibility service has already been created for you. Then, using a terminal, change into the root directory. Navigate to the location where you cloned the source, and select GlobalActionBarService. Select the Import project (Eclipse ADT, Gradle, etc.) option: Launch Android Studio by clicking the Studio icon: Using Android Studio, open GlobalActionBarService. The repo contains several Android Studio projects. You can clone the repo that contains the code for this codelab: git clone Using the terminal, create a directory where you'll be working. A device running Android 7.0 (Nougat) connected to the computer you'll use for development.A terminal for executing simple shell commands.This codelab assumes you'll be using the following: Perform a swipe without having to use a swipe gesture.Perform scroll actions without actually scrolling.Adjust the volume without touching the volume buttons on the side of the phone.Power off the device without reaching the actual power button on the side of the phone.The user can touch buttons on this bar to perform the following actions: Your service will overlay a global action bar on the screen. The user has difficulty scrolling or swiping.The user has difficulty reaching the side buttons on a device.You'll build a service for a hypothetical user with the following characteristics: Since this is a sample, the UI is deliberately kept quite basic. The focus in this codelab is to show you how to write a functional accessibility service. The accessibility API is powerful: the code for the service you'll be building is contained in only four files, and uses ~200 lines of code! If you can write a basic Android app, you can develop a similar service. In this codelab, you'll develop a simple service that does a few useful things using the accessibility API. If there is someone you know who has trouble using their device, YOU can develop an accessibility service for that user! What you'll be building Since many users with disabilities have unique needs, Android's APIs for creating accessibility services are open, and developers are free to create accessibility services and distribute them through the Play Store. While Google provides services like Switch Access, Voice Access, and Talkback for Android users, these services cannot possibly serve all users with disabilities. Talkback: a screen reader commonly used by visually impaired or blind users.Voice Access (beta): allows Android users with mobility limitations to control a device with spoken commands.Switch Access: allows Android users with mobility limitations to interact with devices using one or more switches.Examples of common accessibility services It is a long-running privileged service that helps users process information on the screen and lets them to interact meaningfully with a device. What is an Accessibility Service?Īn Accessibility Service assists users with disabilities in using Android devices and apps. This codelab shows you how to create a very simple accessibility service. An accessibility service can communicate to the user on the application's behalf, for example by converting text to speech or providing haptic feedback when a user is hovering on an important area of the screen. Accessibility services are a feature of the Android framework designed to provide alternative navigation feedback to the user on behalf of applications installed on Android devices. |
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