Radioactive decay - waves and particles Study Guide

Voltage, fundamentally, is the electrical potential difference that drives electric current. However, not all voltages behave in the same way, leading to two main types: direct current (DC) and alternating current (AC) voltage. The key difference lies in the direction of the current flow and the polarity of the voltage. Direct voltage (DC) maintains a constant polarity, meaning the positive and negative terminals remain fixed. This causes the electric current to flow in only one single direction through a circuit. Examples of DC voltage sources include batteries, which have a clearly defined positive and negative end. In contrast, alternating voltage (AC) regularly reverses its polarity. This means that the positive and negative terminals switch places periodically, causing the direction of the electric current to also reverse periodically in the circuit. Mains electricity, which powers our homes and businesses, is an example of AC voltage. This cyclical change in polarity happens very rapidly, for instance, 50 times per second in the UK. The choice between DC and AC depends on the application; DC is often used in portable electronic devices, while AC is used for power transmission over long distances due to its ability to be easily transformed to different voltage levels.

Acceleration is the rate at which an object's velocity changes. Velocity is a vector quantity, meaning it has both magnitude (speed) and direction. Therefore, acceleration occurs when an object speeds up, slows down, or changes direction. The standard unit for acceleration is metres per second squared (m/s²). To estimate everyday accelerations, it's helpful to have a sense of common values. For example, the acceleration due to gravity near Earth's surface is approximately 9.8 m/s², often rounded to 10 m/s² for estimations. This means that a freely falling object increases its speed by about 10 metres per second every second. Everyday accelerations vary widely. A car accelerating from rest to motorway speed might experience an average acceleration of 2-5 m/s². A car braking sharply could decelerate at 6-10 m/s². A person walking has very small accelerations, perhaps less than 1 m/s². Understanding these typical ranges allows for making justified estimates. When estimating, you should consider the change in speed and the time taken for that change. For instance, if an object goes from 0 m/s to 10 m/s in 2 seconds, its acceleration is (10-0)/2 = 5 m/s². Knowing approximate speeds and times for various events can help you make reasonable estimates for acceleration magnitudes.