# 6th Std Practical Class 3 – Some important questions and answers

## Magnetic Needle and Coil

1.What do you observe when button is pressed?

The magnetic needle gets deflected. South pole of the needle points towards the coil when kept at A. North pole of the needle points towards the coil when kept at B.

2.Explain why this happens.

When electric current is passed through a coil, it behaves like a magnet (called electromagnet). So the magnetic needle gets deflected because of this magnet

3.What is this type of magnet called? — electromagnet

4.What is the benefit of this type of magnet over permanent magnet?

It can be turned on and off, its strength can be adjusted by increasing or decreasing the current passing through the coil.

## Plastic bag with coins

1.What do you observe after step 1?
Bag sinks

2.What do you observe after step 2?
Bag floats

3.Weight of the bag has increased when air was added.

4. When air is added, mass of the bag increases slightly, but volume increases a lot. So overall density (of bag + coins) decreases. So it floats

5.Units of pressure –
Bar or Pascal or Newton/metre2 (N/m2)

## Heating Copper Sulphate

1.Observation after heating copper sulphate:

Blue crystals of CuSO4 turn into white amorphous powder. Water of crystallization is lost when heated.

2. Observation after adding a drop of water:

White amorphous powder again turns into blue liquid. It regains water of crystallization.

3. Chemical formula of copper sulphate

Crystalline form – CuSO4. 5H2O

Amorphous form – CuSO4

## Try at Home:

Put an iron nail in copper sulphate solution. Leave it undisturbed for 2-3 hours. Observe. Guess what has happened.

## Big and small stones

When water is poured upto 100 cc mark:

1.Volume of water + stones in cylinder A = 100 cc

2.Volume of water in cylinder A = 41 cc

3.Volume of stones in cylinder A = 100 – 41 = 59 cc

4.Volume of water + stones in cylinder B = 100 cc

5.Volume of water in cylinder B = 35 cc

6.Volume of stones in cylinder B = 100 – 35 = 65 cc

7. Which stones (big / small) occupy more total volume?

Small stones occupy more volume!!

8. Why does this happen?

Large stones have bigger air gaps between them. Small stones have smaller air gaps. So they are more densely packed and occupy more total volume.

## Water and Coin

1.What do you observe?
After adding water, coin becomes visible.

Refraction. Light which was not able to reach our eye earlier (no 1) can now bend at the boundary and reach us (no 2) as shown below.

3. Can you give any similar example?
– A rod when put into water appears bent
– Bottom of the bucket appears to come up when we put water in it
– Light bends at the boundary when it enters a prism.

## Ammonium Chloride and Calcium Hydroxide

1.Do you observe any colour change in the litmus paper? Write your observation.

Red litmus turns blue

2.What can we infer from this observation?

The gas that evolves is basic

3.Write 1 use each of Calcium Hydroxide and Ammonium Chloride.

Ca(OH)2 – Whitewash of walls, making acidic soil neutral

NH4Cl – Fertilizers, Dry cell

4.Write any 3 properties of the gas evolved.

Pungent smell, colourless, basic

## Try at Home

Take some lime water (Calcium Hydroxide + water) in a test tube. Add a drop of phenolpthalein. Blow into it with a straw for 1-2 minutes. Observe

## Weight of Stone in Air and Water

1.Weight of the stone in air = 190gm

2.Weight of the stone in water = 120 gm

3.Does the mass of the stone change when it is put in water? — NO

4.Why does the spring balance show different weight in water?

Water applies upward buoyant force on the stone. So the stone pulls the spring balance down with less force.

5.Why did the spring balance show zero weight when the stone touches the bottom?

When the stone touches the bottom, its entire weight is carried by the base of the jar and the spring of the spring balance is not pulled at all. So it shows zero weight.

6.What is the difference in mass and weight?

Mass is the quantity of matter contained in an object. Weight is the gravitational force acting on an object. Mass always remains same, but weight will be different on moon, on Jupiter, etc.

## Milk and Vinegar

1.What do you observe?
White coloured solids are observed.

2.Explain.
Proteins from the milk get separated

3.Is this a physical change or chemical change?
Chemical

4.Is this reversible / irreversible?
irreversible

5.Where do you use similar reaction in our daily life?
Making ‘paneer’ from milk

## Brush and Cylinder

Q1. Why does the brush go inside?

A1. When we tap the cylinder, the cylinder moves forward. But brush remains in its position due to inertia. So it goes inside.

Q2. What do you observe?

A2. The coin falls forward.

Q3. Explain why this happens

A3. When the car is moving, the coin is also moving. When the car stops, the coin continues to move due to inertia. So it falls forward.

## Try at home

Use: 10 one-rupee coins, scale

1.Find the thickness of one coin. Explain your method.
2.Find the diameter of one coin.
3.Will the accuracy of the answer change if we use 20 coins? Why?
4.One metre = ________cm = ________ mm
5.Least count of your plastic scale = ________

## Mixing two liquids

Q1) 500 ml water + 500 ml water = 1000 ml

Q2) 500 ml water + 500 ml Milk= 1000 ml

Q3) 500 ml water + 500 ml oil = 1000 ml

Q4) 500 ml water + 500 ml alcohol = Less than 1000 ml
Why: Alcohol gets dissolved in water. So alcohol molecules occupy inter molecular space between water molecules.

Q5) How to separate a mixture of water + alcohol?
Distillation.

Q6) 500 gm water + 500 gm alcohol = 1000 gm
Why? Law of conservation of mass. Even if alcohol gets dissolved, its mass will be still there. So total mass will be 1000 gm

Q7) How to  separate immiscible liquids?
Separating funnel.

## Identify the methods of separation

1. Distillation. Useful to separate two liquids which get dissolved into each other and cannot be separated by separating funnel. Eg. Water and alcohol. Distilled water is the purest water.
2. Separating Funnel – for immiscible liquids
3. Chromatography. Used to separate various partials (chemicals) present in a given coloured ink.

## Heart

1. Write flow of blood through various compartments of heart in sequence.
Right atrium –> Right ventricle –> Lungs–>
Left atrium –> Left ventricle

2. Arteries carry pure blood. Pulmonary artery carries impure blood.

3. A person has blood group A+. What is the meaning of ‘+’. He can donate the blood to whom?
‘+’ means a protein called ‘Rh’ is present in the blood.
A+ can donate blood to A+ or AB+

4. Fish heart has 2 chambers. Turtle has 3.