## Archive for April, 2011

### Ohm’s Law

Friday, April 29th, 2011

We are going to investigate the relationship between voltage, current and resistance in an electrical circuit.  This is called Ohm’s Law.   This might be useful to read first.

Log on to the online circuit construction kit we have been using in class.  Build a circuit containing 1 battery and 1 resistor in series.  Add in an ammeter and a voltmeter.  REMEMBER – ammeters in series and voltmeters in parallel.  Record the values for current, voltage and resistance in this table. Ohm’s Law data

Now change the resistance.  Record the data for current and voltage in your table.  Collect at least 10 pieces of data – or more if you need to, until you see a pattern emerging.  Add in another battery, and take some more readings.  Keep adding in batteries and recording data.  Can you come up with a relationship between each of these three quantities?

Using excel, draw a graph of voltage against current.  Add a trendline, label axes, give a title.  What does the gradient of the line tell us?

### Refraction

Friday, April 29th, 2011

refraction by the_green_squirrel

All waves refract.  This means that they change speed as they travel from one medium to another.  For example, light waves travel faster in air than they do in water.  This means the pencil in the glass of water looks like the picture on the right.  For a full explanation of refraction, read this.  Hopefully you now understand the concept.  If not, ask this archer fish to explain it to you!

We will do a lab to investigate refraction of light as it passes through glass and perspex, and to determine the refractive indices of these substances.  This handout (thank you Mr Duckworth) explains in more detail. Grade-9-Integrated-Science-Waves-Topic-refraction1

You will be required to submit the data tables, calculations and graphs for this lab only.  Refer to this rubric: FINALRubric DCP

### Reflection

Friday, April 29th, 2011

wing mirror by Izzard on flickr

All waves are reflected when they hit a surface or barrier.  The angle at which the wave is reflected is not random, but predictable.  We will investigate angles of incidence (i) and angles of reflection (r) of light waves hitting a plane mirror and try to answer these questions about light and reflection:-

• Light travels in straight lines.  What evidence can you think of that shows this?
• What is a virtual image?
• What does laterally inverted mean?

### Waves questions

Tuesday, April 26th, 2011

The distance between repeating parts of the pattern (the length of each single wave) is known as the wavelength (l).  Wavelengths can be measured from anywhere to the next identical part of the wave.

Frequency is a measure of how often something happens in one second. The symbol of frequency is f and the units are hertz (Hz). The relationship between velocity, frequency and wavelength is:

Velocity (m/s) = frequency (Hz) x wavelength (m)

Light waves travel much faster than sound waves. The speed of a set of waves can be found by using information about the distance travelled and time taken or from information about the frequency and wavelength.

Distance, speed and time are connected by:

Speed (m/s)   =   Distance (m) / time (s)

Example An echo takes 1.5 s to reflect from the front wall of a school building 250m away. What is the speed of sound in air?

Distance for echo = 2 x 250 m = 500 m                                Time taken   = 1.5 s

Speed = distance/time = 500/1.5 = 333m/s

This method is practical at school only for the measurement of the speed of sound.

Example Capital Radio broadcasts throughout the London area using radio waves of frequency 1548kHz, travelling at 300000km/s. To what wavelength would you tune a radio to receive Capital programmes?

Speed   = 300000km/s = 300000000m/s                  Frequency = 1548 kHz (1 548 000 Hz)

Wavelength = speed/frequency  = 300 000 000/1 548 000 = 194 m

Using your knowledge of the wave equation, and the relationship between frequency and time [f = 1/T], answer the following questions:-

1. If the waves in the ocean are timed so that they come to shore every 1.74 seconds, what is the frequency of these waves? (Show your working and don’t forget units).
2. A radio wave has a frequency of 2 MHz (2 MegaHertz = 2 000 000 Hz). Calculate the time period between successive waves.
3. A radio station broadcasts with a wavelength of 160m. If the velocity of the radio signal is 3 x 108 m/s, calculate the frequency of the wave.
4. If all the 1.2 billion people in China jump up and down at the same time, they will create a shock wave that will travel around the Earth in all directions.  This wave will focus and peak on the other side of the Earth, exactly opposite China (around California).  If the circumference of the Earth is 40 000km and the speed of sound on the Earth’s surface is 2850m/s, calculate how long it will take for California to crumble into the sea due to the shock wave.

Here are some more practice questions for you to try. We will then have an assessment on this next week. Wave equation practice questions

### Current electricity

Monday, April 25th, 2011

There are LOTS of cool links coming up in the blog post.  Explore them.  Try them out.  You will learn stuff!

Tim and Moby at brainpop have lots to say on this topic.  Here are links to one, two, three of their videos.

Here is Mr Dickinson’s “soldier’s marching” analogy: Electric Circuit

This site has really good, easy to follow information on all matters concerning electric circuits.  We will use this online circuit construction site as well.  And watch this:

### Theoretical genetics

Wednesday, April 20th, 2011

This is the fun stuff – working out genetics problems.  Before the fun stuff comes the groundwork – learning definitions.  Know the meaning of the following terms.

genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterzygous, carrier, test cross, sex linkage

Here is Mr Taylor’s presentation on this section.  Use the links suggested for question practice.  The more problems you solve, the easier they become 🙂

### What is a wave?

Wednesday, April 20th, 2011

sine wave by bdu on flickr

New topic – yay!  We’ll learn about waves – which is very topical at the moment considering all the earthquakes in Japan.  Before we get on to seismic waves we need to have a basic understanding of what a wave is.  Here are some of the points we’ll try and answer:-

• What is a wave?
• What is the difference between transverse and longitudinal waves?
• What are some examples of transverse and longitudinal waves?
• What are the amplitude, frequency and wavelength of a wave?

Anatomy of Waves

We’ll then take a look at the wave equation       v = f λ

This shows us the relationship between speed of a wave v, the time it takes for a particle to vibrate up and down, and the distance between successive waves λ.  You’ll need your calculators as we practice solving problems in class.

### Electricity terms and symbols

Monday, April 18th, 2011

Electricity pillar by Dhammika Heenpella Images of Sri Lanka on flickr

As with any new topic there is new vocabulary to learn.  Find out the meaning of the following electricity terms:-

circuit, series circuit, parallel circuit, current, voltage, potential difference, resistance, diode, ammeter, voltmeter, amperes, volts, ohms

Draw correct symbols for the following pieces of electrical equipment:-

lamp, cell, battery, voltmeter, ammeter, resistor, fuse, switch

Here are a few links to help get you started.  S-coolBBC BitesizeGCSE.com

### Meiosis

Wednesday, April 13th, 2011

genes on parade by Esthr on flickr

Here are some of the terms we will get to terms with in this section 🙂

diploid, haploid, homologous chromosomes, crossing over, non-disjunction, trisomy, karyotyping

• We’ll learn about the process of meiosis, and why it is known as a reduction division.
• We’ll understand how chromosome abnormalities such as Down’s syndrome come about.
• We’ll learn what a karyotype is and how to analyse one.
• And we’ll discuss some ethical issues to do with karyotyping of unborn fetuses.

There are a number of ToK links here, such as balancing the risks of side-effects with preparing for a chromosome abnormality in an unborn child.  There are also questions raised about who should make the decision about whether to perform the karyotype – the parents, doctors, governments?

Here is Mr Taylor’s presentation on this topic.  And here is a very very very dated but well done video.   Biologix__Meiosis_and_Gamete_Formation

We’ll use this site – The Biology Project – to practise karyotyping.

### Static electricity

Wednesday, April 13th, 2011

Lightning by -Qualsiasi on flickr

Start by watching this brainpop video.   And here is our old friend Bill Nye‘s explanation.

Here are a couple more links to some useful information:- this one from enchanted learning and this one from science made simple.

Now can you explain how lightning happens?