The process of adding impurities to a pure semiconductor is called doping. The doped material is referred as extrinsic semiconductor. Doping is done to generate either a surplus or a deficiency in valence electrons.

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Which of the following items is classified under cash flows from investing activities?

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Important Questions on Current Electricity

HARD

Physics>Electricity and Magnetism>Current Electricity>Electric Current

When photon of energy

4.0 e V

strikes the surface of a metal

A,

the ejected photoelectrons have maximum kinetic energy

T_{A} e V

and de-Broglie wavelength

λ_{A} .

The maximum kinetic energy of photoelectrons liberated from another metal

B

by photon of energy

4.50 e V

T_{B} = (T_{A} - 1.5) e V .

If the de-Broglie wavelength of these photoelectrons

λ_{B} = 2 λ_{A},

then the work function of metal

B

is:

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

Describe the DDT biomagnification occurring in an aquatic food chain. State the negative effects the process has on the organisms at the last trophic level of the food chain.

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

Explain energy flow in ecosystem.

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

If the light of wavelength $412.5 nm$ is incident on each of the metals given below, which ones will show photoelectric emission and why?

Metal	Work Function(eV)
Na	1.92 eV
K	2.15 eV
Ca	3.20 eV
Mo	4.17 eV

EASY

Physics>Electricity and Magnetism>Current Electricity>Electric Current

If 20J of energy is trapped at producer level, then how much energy will be available to peacock as food in the following chain?
plant

\to

mice

\to

snake

\to

peacock

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

What is photoelectric effect?

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

Give a diagrammatic representation of energy flow through different trophic levels.

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

What is work function?

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

How is the detritus food chain connected with the grazing food chain in a natural ecosystem?

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

What is a trophic level in an ecosystem ? What is ‘standing crop’ with reference to it?

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

Explain the role of the ‘first trophic level’ in an ecosystem.

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Physics>Electricity and Magnetism>Current Electricity>Electric Current

A $10 V$ cell of negligible internal resistance is connected in parallel across a battery of emf $200 V$ and internal resistance $38 Ω$ as shown in the figure. Find the value of current in the circuit.

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