In Figure, two parallel plates are shown, separated by $25 \mathrm{~cm}$. Copy the diagram and draw field lines to represent the field between the plates.

The electric field lines representing the electric field intensity between parallel plates is drawn as shown in figure below. As B is at higher potential 2 kV and A is at lower potential, so the direction of electric field lines will be from B to A .

In Figure, two parallel plates are shown, separated by $25 \mathrm{~cm}$. What is the electric field strength at $C$, and at $\mathrm{D}$ ?

Electric field strength between parallel plates is uniform, so both points has the same value. Given here, Potential difference V = 2 kV . Separation, d = 25 cm . The relation between electric field, separation and electric potential is given by E = V d . Putting the given values, we get E = 2000 25 × 10 - 2 = 8 kV m - 1

In Figure, two parallel plates are shown, separated by $25 \mathrm{~cm}$. Calculate the electric force on a charge of $+5 \mu \mathrm{C}$ placed at $\mathrm{C}$. In which direction does the force act?

Electric field strength between parallel plates is uniform, so both points has the same value. Given here, Potential difference V = 2 kV . Separation, d = 25 cm . Charge Q = 5 μC The relation between electric field, separation and electric potential is given by E = V d . Putting the given values, we get ⇒ E = 2000 25 × 10 - 2 = 8 kV m - 1 Now, electric force is given by F = E Q = 8 × 10 3 × 5 × 10 - 6 = 0 . 4 N acting towards the left.

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Air is usually a good insulator. However, a spark can jump through dry air when the electric field strength is greater than about $40000 \mathrm{~V} \mathrm{~cm}^{-1}$. This is called electrical breakdown. The spark shows that electrical charge is passing through the air-there is a current. (Do not confuse this with a chemical spark such as you might see when watching fireworks; in that case, small particles of a chemical substance are burning quickly.)

The highest voltage reached by the live wire of a conventional mains supply is $325 \mathrm{~V}$. In theory (but DO NOT try this), how close would you have to get to a live wire to get a shock from it?

Important Questions on Uniform Electric Fields

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Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 21 - Uniform Electric Fields>Questions>Q 8

Air is usually a good insulator. However, a spark can jump through dry air when the electric field strength is greater than about $40000 \mathrm{~V} \mathrm{~cm}^{-1}$. This is called electrical breakdown. The spark shows that electrical charge is passing through the air-there is a current. (Do not confuse this with a chemical spark such as you might see when watching fireworks; in that case, small particles of a chemical substance are burning quickly.)

Estimate the voltage of a thundercloud from which lightning strikes the ground $100 \mathrm{~m}$ below.

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Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 21 - Uniform Electric Fields>Questions>Q 9

In Figure, two parallel plates are shown, separated by $25 \mathrm{~cm}$.

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Copy the diagram and draw field lines to represent the field between the plates.

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AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 21 - Uniform Electric Fields>Questions>Q 9

In Figure, two parallel plates are shown, separated by $25 cm$ . What is the potential difference between points A and B?

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Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 21 - Uniform Electric Fields>Questions>Q 9

In Figure, two parallel plates are shown, separated by $25 \mathrm{~cm}$.

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What is the electric field strength at $C$, and at $\mathrm{D}$ ?

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AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 21 - Uniform Electric Fields>Questions>Q 9

In Figure, two parallel plates are shown, separated by $25 \mathrm{~cm}$.

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Calculate the electric force on a charge of $+5 \mu \mathrm{C}$ placed at $\mathrm{C}$. In which direction does the force act?

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AS and A Level

IMPORTANT

Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 21 - Uniform Electric Fields>Questions>Q 10

A particle of charge $+2 \mu \mathrm{C}$ is placed between two parallel plates, $10 \mathrm{~cm}$ apart and with a potential difference of $5 \mathrm{kV}$ between them. Calculate the field strength between the plates, and the force exerted on the charge.

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Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 21 - Uniform Electric Fields>Questions>Q 11

We are used to experiencing accelerations that are usually less than $10 \mathrm{~m} \mathrm{~s}^{-2}$. For example, when we fall, our acceleration is about $9.81 \mathrm{~m} \mathrm{~s}^{-2}$. When a car turns a corner sharply at speed, its acceleration is unlikely to be more than $5 \mathrm{~m} \mathrm{~s}^{-2} .$ However, if you were an electron, you would be used to experiencing much greater accelerations than this. Calculate the acceleration of an electron in a television tube where the electric field strength is $50000 \mathrm{~V} \mathrm{~cm}^{-1}$. (Electron charge $-e=-1.6 \times 10^{-19} \mathrm{C} ;$ electron mass $m_{\mathrm{e}}=9.11 \times 10^{-31} \mathrm{~kg} .$ )

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Physics for Cambridge International AS & A Level Coursebook 3rd Edition Digital Access>Chapter 21 - Uniform Electric Fields>Questions>Q 12

Use a diagram to explain how the electric force on a charged particle could be used to separate a beam of electrons $\left(\mathrm{e}^{-}\right)$ and positrons $\left(\mathrm{e}^{+}\right)$ into two separate beams. (A positron is a positively charged particle that has the same mass as an electron but opposite charge. Positron-electron pairs are often produced in collisions in a particle accelerator.)

Important Questions on Uniform Electric Fields

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