Electrical and Magnetic Properties — Revision Notes

⚡ 30-Second Revision

Electrical Properties:\n * Conductors: $E_g \approx 0$, high conductivity, conductivity $\downarrow$ with $T \uparrow$. Ex: Cu, Ag.\n * Insulators: Large $E_g (>3 \text{ eV})$, very low conductivity. Ex: Diamond, Plastic.\n * Semiconductors: Small $E_g (0.5-3 \text{ eV})$, intermediate conductivity, conductivity $\uparrow$ with $T \uparrow$. Ex: Si, Ge.\n * n-type: Doped with Group 15 (donor), majority electrons. Ex: Si + P.\n * p-type: Doped with Group 13 (acceptor), majority holes. Ex: Si + B.\n- Magnetic Properties:\n * Diamagnetic: All paired electrons, weakly repelled. Ex: H$_2$O, NaCl.\n * Paramagnetic: Unpaired electrons, weakly attracted, temporary. Ex: O$_2$, Cu$^{2+}$.\n * Ferromagnetic: Unpaired electrons, domains, strongly attracted, permanent. Ex: Fe, Co, Ni. Loses magnetism above Curie Temp ($T_c$).\n * Antiferromagnetic: Unpaired electrons, antiparallel equal moments, net zero. Ex: MnO. Loses order above Néel Temp ($T_N$).\n * Ferrimagnetic: Unpaired electrons, antiparallel unequal moments, net weak. Ex: Fe$_3$O$_4$. Loses magnetism above Curie Temp ($T_c$).

2-Minute Revision

The electrical and magnetic properties of solids are determined by their electron behavior. Electrically, solids are classified by their energy band structure. Conductors have overlapping valence and conduction bands ($E_g \approx 0$), allowing free electron flow; their conductivity decreases with temperature.

Insulators have a large forbidden energy gap ($E_g > 3 \text{ eV}$), preventing electron movement. Semiconductors have a small band gap ($0.5-3 \text{ eV}$), leading to intermediate conductivity that increases with temperature or doping.

Doping with Group 15 elements creates n-type semiconductors (majority electrons), while Group 13 elements create p-type (majority holes). \n\nMagnetically, materials are classified by electron spin alignment.

Diamagnetic substances have all paired electrons and are weakly repelled. Paramagnetic substances have unpaired electrons, are weakly attracted, but lose magnetism when the field is removed. Ferromagnetic materials have strong, permanent magnetism due to aligned domains of unpaired electrons (e.

g., Fe), losing it above the Curie temperature. Antiferromagnetic materials have antiparallel, equal magnetic moments (net zero). Ferrimagnetic materials have antiparallel, unequal moments, resulting in a net, weaker magnetism (e.

g., Fe$_3$O$_4$).

5-Minute Revision

Let's consolidate the key aspects of electrical and magnetic properties of solids for NEET. \n\nElectrical Properties:\nAt the heart of electrical properties is Band Theory. Atomic orbitals in solids form continuous energy bands: the valence band (VB) and the conduction band (CB), separated by a **forbidden energy gap ($E_g$)**.

\n* Conductors: $E_g \approx 0$ (bands overlap). Electrons move freely. High conductivity ($10^4-10^7 \text{ ohm}^{-1}\text{m}^{-1}$). Conductivity decreases with increasing temperature (e.g., Cu, Ag).

\n* Insulators: Large $E_g (>3 \text{ eV})$. Electrons cannot jump to CB. Very low conductivity ($10^{-10}-10^{-20} \text{ ohm}^{-1}\text{m}^{-1}$) (e.g., Diamond, Glass). \n* Semiconductors: Small $E_g (0.

5-3 \text{ eV})$. Some electrons jump to CB at room temperature. Intermediate conductivity ($10^{-6}-10^4 \text{ ohm}^{-1}\text{m}^{-1}$). Conductivity increases with increasing temperature (e.g., Si, Ge).

\n * Doping: Adding impurities to enhance conductivity. \n * n-type: Doped with Group 15 elements (P, As) into Group 14 (Si). Extra electrons are majority carriers. \n * p-type: Doped with Group 13 elements (B, Al) into Group 14 (Si).

Holes are majority carriers. \n\nMagnetic Properties:\nThese arise from electron spin and orbital motion, creating magnetic moments. \n* Diamagnetic: All electrons are paired. Net magnetic moment is zero.

Weakly repelled by external magnetic field. (Ex: H$_2$O, NaCl). \n* Paramagnetic: Contains unpaired electrons. Individual magnetic moments are random. Weakly attracted to external magnetic field, but magnetism is temporary and disappears when field is removed.

(Ex: O$_2$, Cu$^{2+}$). Paramagnetism decreases with increasing temperature. \n* Ferromagnetic: Contains unpaired electrons. Strong, spontaneous alignment of magnetic moments within domains. Strongly attracted to external magnetic field and retains magnetism even after field removal (permanent magnets).

(Ex: Fe, Co, Ni). Loses ferromagnetism above **Curie Temperature ($T_c$)** and becomes paramagnetic. \n* Antiferromagnetic: Contains unpaired electrons. Magnetic moments in domains are aligned antiparallel and are equal in magnitude, resulting in a net zero magnetic moment.

(Ex: MnO). Loses order above Néel Temperature ($T_N$). \n* Ferrimagnetic: Contains unpaired electrons. Magnetic moments in domains are aligned antiparallel but are unequal in magnitude, resulting in a net, but weaker, magnetic moment.

(Ex: Magnetite, Fe$_3$O$_4$). Loses ferrimagnetism above Curie Temperature ($T_c$). \n\nMini-Example: If you have a silicon crystal and add a tiny amount of arsenic, you get an n-type semiconductor because arsenic (Group 15) donates extra electrons.

If you then put this material in a strong magnetic field, its magnetic behavior would likely be diamagnetic if all its electrons are paired, or paramagnetic if there are any unpaired electrons from the Si or As atoms, but it won't be ferromagnetic unless it contains specific transition metals.

Prelims Revision Notes

I. Electrical Properties (Band Theory)\n1. Energy Bands: Atomic orbitals form Valence Band (VB) and Conduction Band (CB).\n2. **Forbidden Energy Gap ($E_g$):** Energy difference between VB and CB.

\n * Conductors: $E_g \approx 0$ (VB & CB overlap). High conductivity ($10^4-10^7 \text{ ohm}^{-1}\text{m}^{-1}$). Conductivity $\downarrow$ with $T \uparrow$. Ex: Cu, Ag.\n * Insulators: Large $E_g (>3 \text{ eV})$.

Very low conductivity ($10^{-10}-10^{-20} \text{ ohm}^{-1}\text{m}^{-1}$). Ex: Diamond, Glass.\n * Semiconductors: Small $E_g (0.5-3 \text{ eV})$. Intermediate conductivity ($10^{-6}-10^4 \text{ ohm}^{-1}\text{m}^{-1}$).

Conductivity $\uparrow$ with $T \uparrow$. Ex: Si, Ge.\n3. Types of Semiconductors:\n * Intrinsic: Pure semiconductor. Conductivity due to thermal excitation.\n * Extrinsic (Doped): Conductivity enhanced by impurities.

\n * n-type: Doped with Group 15 elements (P, As, Sb) into Group 14 (Si, Ge). Donor impurities. Majority carriers: Electrons.\n * p-type: Doped with Group 13 elements (B, Al, Ga) into Group 14 (Si, Ge).

Acceptor impurities. Majority carriers: Holes.\n\nII. Magnetic Properties (Electron Spin)\n1. Origin: Unpaired electrons (spin & orbital motion) create magnetic moments.\n2. Classification:\n * Diamagnetic: All electrons paired.

Net magnetic moment = 0. Weakly repelled by external field. No residual magnetism. Ex: H$_2$O, NaCl, Benzene.\n * Paramagnetic: Unpaired electrons. Random moments. Weakly attracted by external field.

Magnetism temporary (disappears when field removed). Paramagnetism $\downarrow$ with $T \uparrow$. Ex: O$_2$, Cu$^{2+}$, Fe$^{3+}$.\n * Ferromagnetic: Unpaired electrons. Strong, spontaneous alignment in domains.

Strongly attracted by external field. Retains magnetism (permanent). Ex: Fe, Co, Ni, CrO$_2$. Loses ferromagnetism above **Curie Temperature ($T_c$)** (becomes paramagnetic).\n * Antiferromagnetic: Unpaired electrons.

Antiparallel and equal alignment of moments in domains. Net magnetic moment = 0. Ex: MnO, FeO. Loses order above **Néel Temperature ($T_N$)** (becomes paramagnetic).\n * Ferrimagnetic: Unpaired electrons.

Antiparallel but unequal alignment of moments in domains. Net weak magnetic moment. Ex: Fe$_3$O$_4$ (magnetite), MgFe$_2$O$_4$. Loses ferrimagnetism above **Curie Temperature ($T_c$)** (becomes paramagnetic).

Vyyuha Quick Recall

To remember the magnetic materials and their properties, think of 'D-P-F-A-F':\nDon't Play Football After Four\n* Diamagnetic: Don't attract (repel), Double (paired) electrons.

\n* Paramagnetic: Partially attract, Paired-not (unpaired) electrons, Permanent-not (temporary).\n* Ferromagnetic: Fiercely attract, Fixed (permanent) magnetism, Form domains.

\n* Antiferromagnetic: Anti-parallel equal, Absent (zero) net magnetism.\n* Ferrimagnetic: Ferrites, Fairly attract, Forced anti-parallel unequal.