Clock Puzzles 7 [With Answers]

Puzzle 1:

Answer: 6:06

Explanation: From Left to Right, The time on the watches increases by 2 hours 3 minutes, then decreases by 1 hour 16 minutes, alternately.

Puzzle 2:

Answer: 3:36

Explanation: On each watch, the time shown contains two digits that are the same.

Puzzle 3:

Answer: 6:45

Explanation: From left to right, add 1 to the value of each digit on the watch, and rotate the digits one place to the left.

Puzzle 4: Calculate the angle between the two hands of clock when the clock shows 4 : 20 p.m. ?

A) 5 degrees               B) 10 degrees

C) 15 degrees             D) 25 degrees

Answer: B) 10 degrees

Explanation: Since at 4 : 20 the minute hand will be at 4 and the angle between them will be same as the distance covered in degree by the hour hand in 20 minutes.

Required angle = distance of hour hand = speed × time = ½ × 20 =10 degrees.

Puzzle 5: If a Siren sounds for every 5 seconds, how many times will it sound in ¾ of an hour?

A) 541 times                B) 540 times

C) 450 times                D) 275 times

Answer: A) 541 times

Explanation: There are 60 minutes in an hour.

In ¾ of an hour there are (60 × ¾) minutes = 45 minutes.

In ¾ of an hour there are (60 × 45) seconds = 2700 seconds.

Siren sounds for every 5 seconds.

In 2700 seconds 2700/5 = 540 times.

The count start after the first sound, the Siren will sound 541 times in ¾ of an hour.

Ohm’s law

General form of Ohm’s law:

At a constant temperature potential difference across a conductor is directly proportional to the current passing through it

V α I V = RI

Ohm’s law is material dependent because it is defining resistance of the material. Those which obeys ohm’s law and are known as ohmic or linear conductor, otherwise non-ohmic or nonlinear conductor.

Proof: Current density (J) α E (Applied electric field)

J α E

j = σE

σ = Conductivity

We know that

σ = 1/ρ

R = ρ * 1/A

ρ = RA/l

1/ρ = l/RA = σ

J = 1/A, E = v/l

  

Limitations:

• It is valid only at constant temperature.
• It can be applied only to bi – lateral elements [linear elements].

Clock Puzzles 7

Puzzle 1:

Puzzle 2:

Puzzle 3:

Puzzle 4: Calculate the angle between the two hands of clock when the clock shows 4 : 20 p.m. ?

A) 5 degrees                 B) 10 degrees

C) 15 degrees               D) 25 degrees

Puzzle 5: If a Siren sounds for every 5 seconds, how many times will it sound in ¾ of an hour?

A) 541 times                 B) 540 times

C) 450 times                 D) 275 times

Diameter

The locus of the mid-points of a system of parallel chords of a conic is known as its diameter.

Equation of diameter of a parabola:

Let y = mx + c be a system of parallel chords of the parabola y² = 4ax.

Here, m is a constant and c is a variable.

The line y = mx + c meets the parabola y² = 4ax in the points say P and Q whose ordinates (say y₁ and y₂) are the roots of the equation.

∴ 

my² - 4ay + 4ac = 0.

∴ y₁ + y₂ = 4a/m.

Let M (h, k) be the mid-points of PQ. Then,

k = 2a/m.

Hence, the locus of (h, k) is y = 2a/m.

Puzzles 3 [With Answers]

Puzzle 1: You are wandering around in the desert and are exhausted. You meet a nomad and ask him for the way out.

There are only two choices to pick: either go to the left or to the right. One way leads to an oasis and the other way is "the road to death".

However, the nomad is a liar and you cannot trust him. But you know for certain that he is systematically lying:

If he lies on one day, he will not lie the following day and vice versa. You can ask him only one question and he will answer with "yes" or "no".

What question do you ask him in order to survive?

Answer: "If I had asked you yesterday about the way to the oasis, would you have told me to take the way to the left?"

If the nomad answers with "yes", pick the right way, otherwise go to the left.

Puzzle 2: Add the following numbers:

Take 1000 and add 40. Now, add another 1000. Now add 30. Now, add 1000 again. Add 20. And add 1000 again. And an additional 10.

Answer: Do you think the result is 5000?

Actually, it is not. The correct result is 4100.

Puzzle 3: Can you place six X's on a Tic Tac Toe board without making three-in-a-row in any direction?

Answer:

Puzzles 4: All day I move to and fro,

You watch me daily and

You make me dance all the time to pass by.

Who am I?

Answer:  DOOR

Explanation: All day DOOR move to and fro,

We watch Door daily and

We make DOOR dance all the time to pass by.

Puzzle 5: If

526 = 9

834 = 9

Then

716 =?

A. 20 B. 15 C. 9 D. 12

Answer: D. 12

Interhalogen compounds:

Reaction between two different halogens

Types: XX’, XX’₃, XX’₅ and XX’₇

X - Halogen of larger size, more electropositive

X’- Halogen of smaller size

Preparation:

• Direct combination.
• Product depends on the concentrations of the reactants.
  Cl₂ + F₂  → 2ClF
  Cl₂ + 3F₂ → 2ClF₃

Properties:

• Covalent molecules
• Diamagnetic
• Volatile solids/liquids {except ClF which is a gas}
• More reactive than halogens {except Fluorine} because X - X’ bond is weaker than X - X bond.
• All are polar due to difference in their electronegativity. Some compounds partially ionize in solution.
  For example:   2ICl → I⁺ + ICl²⁻

Structure:

•  XX₃ - bent T shape
• XX₅ - Square pyramida
•  IF₇ - Pentagonal bipyramidal

Uses:

• Some interhalogens, such as BrF₃, IF₅, and ICl, are good halogenating agents.
  Ex: U + 3ClF₃ → UF₆ + 3ClF
• Iodine monochloride helps to measure the saturation of fats and oils, and as a catalyst for some reactions.
• A number of interhalogens, including IF₇, are used to form polyhalides.