Kpk Physics 2021 — Solved MCQs

Question 1

A one microfarad of a TV is subjected to 4000 V potential difference, The energy Stored in capacitor is_.

Accepted Answer

A. 8 J — To calculate the energy stored in a capacitor, you can use the formula:E = 1/2 CV2E = 1/2 (1x10-6)(4000)2E= 8J

Question 2

Whonie one of the given are ohmic materials?

Accepted Answer

D. Metals — All metals are ohmic conductors and all semiconductors are non-ohmic materials.Ohmic material are those material that conduct electricity and obey ohms law

Question 3

A magnetic field B exerts a force of 10 N on a current carrying conductor of length 0.5 m. If 50 A current flows in a conductor L then the strength of field is......

Accepted Answer

C. 0.4 T — F = BILB= F/IL= 10/(0.5)(50)= 0.4 T

Question 4

When a wire is stretched and its radius becomes r / 21 then its resistance will be.

Accepted Answer

B. 4R

Question 5

Which one of the given device is always connected in series to a P.D. source?

Accepted Answer

B. Ammeter — Ammeter is used to measure the current flowing through a component/circuit. Since, current remains same in series connection and also the resistance of an ammeter is very small due to which it doesn't affect the current to be measured. So, an ammeter is connected in series to measure current.

Question 6

The peak value of sinusoidal voltage in AC circut is 50. The rms Value of voltage is roughly equal to _.

Accepted Answer

C. 35 V — Vrms=Vpeak/√2=50/√2= 35V

Question 7

The angular momentum of electronic in the 3rd Orbit of H- atom is_.

Accepted Answer

C. 3h / 2π. — L=mvr=nh/2πAs n=3so,L=3h/2π

Question 8

A 96 gm sample of radioactove nuclide is Placed container Afar 12 min, only 6 gm of sample is left undecayed. What is the half-life radioactive nuclide?

Accepted Answer

D. 3 min — Calculate no of half lives:After one half life: 96=> 48After 2 half life: 48=> 24After 3 half life: 24=> 12After 4 half life: 12=> 6total half lives are 4.Half life = Total time/ no of half lives.= 12/4=3 min

Question 9

The energy of electronic in the excited state n = 3 is _.

Accepted Answer

D. -1.5 eV — As,E = -13.6/n2Here, n=3,= -13.6/32= -1.5eV

Question 10

The device which converts A.C into D.C is Called _.

Accepted Answer

A. Diode — Diod is used to conver AC to DC.

Question 11

The hall-life of a radioactive material is_.

Accepted Answer

C. T1 / 2 = log2 / λ — T1 / 2 = log2 / λ is the right formula.

Question 12

If the K.E of fee electron doubles,its de Broglie wavelength changes by the factor.

Accepted Answer

B. 1/√2 — When the kinetic energy (KE) of a free electron doubles, its de Broglie wavelength changes by a factor of 1/√2. This is because the de Broglie wavelength is proportional to 1/KE, so when KE doubles, the wavelength becomes proportional to 1/2KE

Question 13

The positron has charge which is in magnitude equal to the charge on-------

Accepted Answer

D. All these — Positron has equal cahrge as proton, electron and B-particle have charge.

Question 14

A current in a primary coil changes from 5.0 A to 6.0 in 6.0 sec an induced emf of 10.0 V is produced in the nearby placed secondary coll. The co-efficient of mutual induction is........

Accepted Answer

D. 60H — As,E = M dI/dtM = E/dI/dtM = E dt/ dIM = 10(6)/ 1M = 60H

Question 15

In the reaction »zXA > »°ZX-1 +Y + neutron+Q; Y stands for:

Accepted Answer

B. positron — This reaction is B-decay and Positron is released in B-decay

Question 16

Most of the electrons in the base of NPN transistor flow:

Accepted Answer

B. Into the collector — Majority of Electrons: Most of the electrons injected into the base from the emitter do not recombine in the base. Instead, they are swept into the collector by the electric field of the reverse-biased collector-base junction.Current Flow: This results in a majority of the electrons flowing from the base into the collector, contributing to the collector current.Therefore, in an NPN transistor, most of the electrons in the base flow into the collector.

Question 17

Which one of the following materials is weakly attracted by magnet?

Accepted Answer

C. Paramagnetic — Ferromagnetic materials: These materials, such as iron, cobalt, and nickel, have strong magnetic properties. They can become permanently magnetized and are strongly attracted to magnets.Diamagnetic materials: These materials, such as copper, silver, and gold, are weakly repelled by a magnetic field. They do not retain magnetic properties when the external magnetic field is removed.Paramagnetic materials: These materials, such as aluminum, platinum, and certain metal oxides, are weakly attracted by a magnetic field. They have unpaired electrons that align with the magnetic field but do not retain any magnetization when the external field is removed.So, paramagnetic materials are weakly attracted by a magnet.

Question 18

Let a charge of 1 nano-coulomb lies at the centre of a surface,the number of electric field lines leaving the surface are:

Accepted Answer

D. 113 — As Φ = q/E0= 1x10-9 / 8.854x10-12= 1.3x102= 113

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