F4a Physics (t3)

WAVE MOTION: REFLECTION, REFRACTION

Electromagnetic spectrum

The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. 

From low to high frequency these are: 

• radio waves, 

• microwaves, 

• infrared, 

• visible light, 

• ultraviolet, 

• X-rays, and 

• gamma rays.

The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications.

NOTE: The lower the frequency the longer the wavelength: the higher the frequency the shorter the wavelength.

Electromagnetic waves are transverse waves. That means the electric and magnetic fields change (oscillate) in a plane that is perpendicular to the direction of propagation of the wave. Also note that electric and magnetic fields in an EM wave are also perpendicular to each other.

The simplest and most common electromagnetic waves are transverse. When an electromagnetic wave interacts with an object or material such that it is guided or deflected, it gains a longitudinal component. Even electromagnetic waves traveling through free space can have longitudinal components if set up properly.

Radio waves, gamma-rays, visible light, and all the other parts of the electromagnetic spectrum are electromagnetic radiation. Electromagnetic radiation can be described in terms of a stream of mass-less particles, called photons, each traveling in a wave-like pattern at the speed of light.

·         Sound waves always behave as a longitudinal waves.

·         Light is a transverse wave.

Effects of electromagnetic spectrum waves on living things

Electromagnetic spectrum waves can affect living things in various ways depending on their energy level, with high-energy waves like ultraviolet, X-rays, and gamma rays causing potential cellular damage and DNA mutations, while lower energy waves like radio waves generally have minimal impact unless exposed to very high intensities; visible light is essential for sight and some infrared radiation is perceived as heat by the body.

Activity

Q1. Are electromagnetic waves transverse or longitudinal? 

Q2. What is the electromagnetic spectrum?

 Q3. Write down the seven types of electromagnetic radiation in order of increasing wavelength. 

Q4. State one use for each type of radiation. 

Q5. An electromagnetic wave source produces microwaves 

a) The wave source is adjusted so that it produces EM waves with a lower frequency. What effect does this have on the wavelength of the waves produced? 

b) The wave source is now giving out a different type of electromagnetic radiation. What type of electromagnetic radiation it is now giving out? 

Q6. Select two types of EM radiations and describe effects of over exposure to them 

ECHOS

Echoes are a common everyday scenario. Echoes happen when outgoing sound is reflected off a surface. This is phenomenon is used in ultrasound. 

Sample Practical investigation 

Title: Speed of sound 

Echoes are a common everyday scenario. Echoes happen when outgoing sound is reflected off a surface back to the source. This is phenomenon is used in ultrasound. 

Newton used echoes to estimate the speed of sound in an outdoor corridor at Trinity College, Cambridge.

 A rough measurement of the distance is necessary before proceeding with the experiment. 

Aim: To calculate the speed of sound using echoes. 

Procedure: 

1. The experimenter stands as far away as possible from a large reflecting wall and claps their hands rapidly at a regular rate. 

2. This rate is adjusted until each clap just coincides with the return of an echo of its predecessor, or until clap and echo are heard as equally spaced. 

3. Use a stopwatch to find the time between claps, t. Make a rough measurement of distance to the wall, s. Thus the speed of sound, v = 2 s/t in the first case 

MOTION

Sub-strand 7.2: Motion 

Key Learning Outcome: Students are able to demonstrate an understanding of the Motion and Force and analyze the motion of the object due to the effect of a force. 

Speed is a measurement of how fast an object moves relative to a reference point. It does not have a direction and is considered a magnitude or scalar quantity. Speed can be figured by the formula: 

Speed = Distance/Time. 

Speed is scalar 

Speed relates to how fast something is moving and how fast it moves over a distance.  

• For example, something moving very fast, like a train, can cover a large distance in a short time.  

• Something moving slowly, like a walking man, will travel a very short distance in the same amount of time. An object that is not moving has zero speed 

Velocity is a vector 

Velocity is the rate at which an object changes its position.  

• If something is moving back and forth and always returns to its original position, it has speed but zero velocity because it doesn’t change position. 

Simply velocity is how fast something is moving AND the direction. 

If you want to describe an object's velocity, you mention the speed; e.g. 30 mph, and the direction of say north, or to the right (just two examples). 

Velocity = displacement/time. 

Vector and scalar 

A vector is a quantity or phenomenon that has two independent properties including magnitude and direction. 

Examples of vectors in nature are velocity, momentum, force, electromagnetic fields, and weight. (Weight is the force produced by the acceleration of gravity acting on a mass.) 

Scalar, a physical quantity that is completely described by its magnitude; 

Examples of scalars are volume, density, speed, energy, mass, and time. 

Vector addition 

Vector addition is the process of combining two or more vectors to determine the total or resultant effect. 

Important steps involved in vector addition 

• Starting from where the head of the first vector ends,  

• draw the second vector to scale in the indicated direction.  

• Label the magnitude and direction of this vector on the diagram.  

• Draw the resultant from the tail of the first vector to the head of the last vector.

• Label this vector as Resultant or simply R 

Activity:

Add the vectors and find the resultant (R) of the 2 vector problems below.

Vector Operation

UNIT OF SPEED

Unit of Speed  

• Since speed is express as the total distance covered divided by time, S = 𝑑 𝑡 .Therefore the unit of speed is determined by the unit of distance divided by the unit of time.  

• In the metric system of measurement, the most common units of distance are millimeters, centimeters, meters, kilometers and miles. 1ft = 30.48cm 1 cm = 10 mm 1 m = 100cm 1 m = 1000mm 1km = 1,000m 1 miles = 1.6km = 1609m (commonly used at land distance) 1 nautical miles = 1.151 miles (commonly used at sea distance)  

• For time the most common metric system of measurement are seconds , minutes and hour 60 sec = 1 mins 60 mins = 1 Hour 3600 sec = 1 Hour  

• Common unit of speed are cm/mins, m/s , km/hr , miles / hr , knot (1 knot = 1 nautical mile / hour)  

         Important Unit Conversion steps applied to speed unit (also applied to other physical units) 

I. Identify the unit you have. These are the Starting Units

II. Identify the unit you want. These are the Desired Units.

 III. Identify appropriate unit conversion factor(s). 

IV. Cancel units and perform the math calculations (e.g., multiply, divide). 

V. Evaluate the result