# TS Physical Science Answer Key SSC 2017

#### Section – I

1. Ag, Fe, Zn, Na

2. Change the poles of the magnet or wire

3. n = 4, l= 0 , m = 0, s = 1/2

4.  Person develops Myopia. Person can see nearby objects but not distant objects.

5.

6. We can’t use the same wire as fuse wire. Fuse wire needs to have low melting point in order to break the circuit during overload.

7.

#### Section – II

8. Al + Fe2O3 –> Al2O3 + Fe

Aluminium is a more reactive metal. It reduces iron oxide (hematite) to iron.

9.

Electrons are arranged from lower energy level to higher energy level(Aufbau Principle).

There cannot be more than 2 electrons in an orbital. No two electrons can have all 4 quantum numbers same(Pauli’s Principle)

Degenerate orbitals should be half-filled before pairing up electrons.(Hund’s Rule)

10.

11. (i) Substance C can be neutral.

(ii) Substance B is basic, with phenolphthalein, it will turn pink in colour

12. Any object(light source) kept at the centre of curvature will give inverted image of the same size (as that of the object) on a screen at the centre of curvature. Place a candle at a certain distance from lens. Adjust the screen such that an inverted same size image is obtained. Now, distance between lens and screen is radius of curvature. Half of the radius will give focal length value.

13. Convex lens: Boy is trying to see moon. When object is at infinity, the image is formed at the focus. As both the lenses have same focal length and are separated by a distance of 2f, the image formed by the first lens, becomes the object for the second lens. Thus, for the second lens, object is at its Focus. The boy would see a highly enlarged image of the moon.

#### Section – III

14. Chemical Equation

Zn + 2 HCl –> ZnCl2 + H2

In the balanced chemical equation, 2 moles of HCl gives 1 mole of H2. If we use, 1 mole of HCl, we would get 0.5 moles of H2.

At STP,

1 mole of H2 = 6.023×10^23 molecules

Hence, 0.5 moles of H2 = 3.012 x 10^23 molecules

14. Electron Affinity

Definition : Energy released from a neutral gaseous atom when it accepts an electron in its valence shell.

Factors Affecting E.A: Atomic Radius, Effective Nuclear Charge, Screening Effect, Electronic configuration.

Effective Nuclear Charge is weaker when the valence shell electrons are being located farther away from the nucleus. Lesser the effective nuclear charge, lesser is the electron affinity

Screening Effect is more when there are lots of inner shell electrons. If more inner shells electrons are present, they screen or shield and hence decrease nuclear attraction over valence electrons. More screening effect, less electron affinity.

Electron affinity is lesser if the element has either half-filled electronic configuration and E.A is almost zero if the element has fully-filled  electronic configuration.

15. Hypermetropia and Correction

Person with this defect cannot see nearby objects.

Near Point – The nearest distance at which the lens can form an image on the retina or the minimum distance beyond which a person with hypermetropia can see an object.

Correction

• Person with Hypermetropia can see at & beyond Near Point.
• Person cannot see from 25 cm to Near Point.
• In order to correct Hypermetropia, we should use a lens that can form the image at or beyond near point for an object located within the near point.
• Biconvex lens is suited for this purpose.

Calculation

• object distance, u = -25 cm
• image distance, v = near point distance, -d
• Lens Formula:
• 1/f = 1/v – 1/u
• 1/f = -1/d – (-1/25)
• 1/f = -1/d + 1/25
• 1/f =  -25+d / 25d
• f = 25d/d-25
• As, d is more than 25 cm, focal length will be positive value.

15. Current carrying wire in a magnetic field

When a current carrying wire is placed perpendicular to the magnetic field, a mechanical force is exerted on the conductor.

F = q v b sin(theta)

Direction of movement of the conductor is given by Fleming’s Left Hand Rule.

Fore finger, Middle finger and Thumb of the left hand are held at right angles to each other. Fore finger is aligned with the direction of magnetic field, Middle finger points to the direction of current, then the direction in which thumb points, gives the direction of force on the conductor.

Activity:-

• Suspend a copper wire AB vertically from a support.
• Lower end B of the wire should touch the surface of mercury kept in a vessel.
• Positive terminal of a battery is connected to end A of the wire.
• Circuit is completed by dipping another wire from negative terminal of battery into the mercury vessel
• The entire set is placed perpendicular to a uniform magnetic field using horse shoe magnet
• When current passes through the wire from A to B and magnetic field lines are from left to right, then the wire AB moves in the forward direction. Lower end B moves to new position B’, thus in the circuit, connection is broken.
• Since no current flows in the wire’s new position, mechanical force is not exerted and wire reverts to its original position. Wire makes contact with mercury and current starts to flow in the wire and wire moves forward.
• This motion is repeated until battery gets drained.
• If we reverse, the direction of current, then the wire moves in rear direction.

16. Acids/ Bases have ions

Materials Required: HCl, H2SO4, Acetic acid, Citric acid, NaOH, KOH, NH4OH, Glucose, Alcohol, Graphite Rods, AC plug-220V, Bulb, Electrical wires.

Procedure:-

• Prepare solutions of HCl, H2SO4, Citric acid, Acetic acid,NaOH, KOH, and NH4OH, Glucose, Alcohol.
• Take a beaker and add HCl solution.
• Insert 2 Graphite rods into the solution.
• Connect one of the rod to the AC plug, Connect the other rod to the bulb. Complete the circuit by connecting bulb and AC plug. Use electrical wires for connecting.
• Switch on the current.
• Repeat the same procedure for H2SO4, Citric acid, Acetic acid,NaOH, KOH, NH4OH, Glucose and Alcohol

Observation

• Light bulb glows for all the solutions, except glucose and alcohol.
• Dim glow is seen for acetic acid and citric acid and NH4OH.
• Bright glow is seen for HCl and H2SO4, NaOH, KOH.
• Glucose and alcohol does not have ions, so bulb does not glow.

Inference

• Acids and Bases behave as electrolytes. Acids give H+ ions in solution which results in flow of current. Bases give OH- ions in solution which results in flow of current.
• HCl, H2SO4 are strong acids, i.e., more H+ ions are produced.
• Acetic acid and citric acid are weak acids, i.e., less H+ ions are produced.
• Similarly, NaOH and KOH are strong bases, giving more OH- ions, whereas, NH4OH is a weak base, giving less OH- ions.

Thus, passing of current and glowing of bulb shows that acids and bases have ions.

16. Esterification

Reaction between carboxylic acid and alcohol in presence of conc.H2SO4 —> esters

Materials Required: Acetic acid, Ethanol, Conc.H2SO4, Beakers, Water, Burner, Test-tube

Procedure

1 ml of ethanol is added to 1 ml of ethanoic acid, few drops of Conc.H2SO4 is added and warmed in water bath for few minutes and then poured into a test tube containing water. The resulting mixture has sweet smell. This is due to the formation of ester

17. Focal length Calculation