LIGHT AND HEAT Light What is light u

LIGHT AND HEAT

Light What is light? u It is the form of energy that ____ allows us to see. u Without light we cannot see even if we have eyes. u I can see because there is light.

Light u Some sources of light Torch Sun Fireflies Lamp Candles

Reflection of light We see objects because the object _____ reflects light. This enables our eyes to see the object! Light from the lamp bounces off the table Lamp Eye Light enters our eye

Reflection of Light u Draw arrows to indicate the reflection of light sun

Seeing Through Materials TYPES OF MATERIALS Allow light to pass through Allow a little light to pass through Do not allow light to pass through EXAMPLES

Shadow u u u A shadow is formed when light is partially or blocked completely_____. Shadows can be formed because light travels in a______. straight line Objects that do not allow any light to pass through them darker will cast _____ shadows If a material allows a little light to pass through, how will the shadow be? Objects that allow a little light to pass through them will cast lighter shadows. _____

Shadow u An object can cast shadows of different position shapes depending on the _____ of the light source. light directly above short shadow light from the side longer shadow

Shadow u The size of the shadow will depend on the position of the light source. light closer shorter shadow light further away longer shadow The further the light source is from the longer the shadow formed. object, the _______

Shadow u The size of the shadow will depend on the position of the light source. bigger shadow light closer smaller shadow light further away The nearer the light source is to the bigger object, the _____ the shadow formed.

What have we learnt u u u reflects light or An object can be seen when it ______ when it is a source of light straight line Light travels in a______ Opaque or _____ translucent objects prevent light _______ from passing through and form a ____ shadow The further away the light source from the longer the shadow object, the ____ The nearer the light source to the object, the bigger ____ the shadow.

Time to put on your thinking cap

What would be observed on the white screen if a clear blue plastic sheet is placed in front of the light source? clear blue plastic sheet light source Correct answer

Refer to pg 129

Questions a) Based on the graph, how many object X passed the sensor in 22 seconds? Ans: 5 Object X

Questions b) The light source and the sensor are placed 3 cm above the belt. State whether an object that is less than 3 cm in height can be counted. Give a reason for your answer. Ans: No. An object that is less than 3 cm in height cannot block the light source and thus the light will still reach the light sensor.

Questions c) The set-up can count 20 object X in a minute when the belt is moving at its maximum speed. Suggest one way to count more than 20 object X in a minute without changing the speed of the belt. Ans: Place the objects X nearer to each other on the belt.

Refer to pg 130

Questions a) Two properties of light caused shadows to be formed. One of these properties is light travels in a straight line. State the other property. Ans: Light can be blocked.

Questions b) Is Daisy walking towards or away from the lamp during the period Y shown in the graph? Give a reason for your answer. Ans: Daisy is walking away from the lamp during period Y. A longer shadow will be cast (1/2 m)as more light will be blocked (1/2 m)when Daisy is moving further away from the lamp which is the light source.

Questions c) From the graph, Ken concluded that Daisy was walking at a slower speed during period X compared to Y. Explain how did Ken come to this conclusion. Ans: The time intervals for period X and period Y are the same (2 s). The change in length of the shadow is less for period X than Y. Thus, Ken can conclude that Daisy walked at a slower speed during period X than period Y.

Additional Questions u Pg 88 Q 11 u Pg 111 Q 48 u Pg 122 Q 66

Thank You